how to use an animated gif in asp.net web form

thanks for the comment my html where i have used it is
<div runat="server" id="DivOutput" visible="false">
                <asp:ImageButton ID="ImageAjax" runat="server" ImageUrl="~/Images/ajax-loader.gif"
                    AlternateText="Please wait" Visible="false" />
                <br />
                <asp:Label ID="lblOutput" runat="server" Text="" class="GenericLabel" ForeColor="Red"
                    Visible="true"></asp:Label>
                <br />
                <br />
            </div>

on my code behind in button click event i have

 DivOutput.Visible = true;
            ImageAjax.Visible = true;

the image loads the animation starts for a second or so and then stops

any ideas why

i guess the problem occus on the postback on button click. I found a javascript solution to reload the image on postback but unable to do so. may be i need to do tweak my code for javascript. I am using c# and masterpage. My code is attached. I m trying to  load  the image again on runtime

<%@ Page Title="Life in the UK test - Register" Language="C#" MasterPageFile="~/MasterPageGenericWithSideBar.master"
    AutoEventWireup="true" CodeFile="Register.aspx.cs" Inherits="PL_Register" %>

<%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="asp" %>
<%@ Register Assembly="Telerik.Web.UI" Namespace="Telerik.Web.UI" TagPrefix="telerik" %>
<asp:Content ID="Content1" ContentPlaceHolderID="ContentPlaceHolder1" runat="Server">
    <script type="text/javascript">
        document.title = "Life in the UK Test-Register";
    </script>
    <telerik:RadScriptManager ID="RadScriptManager1" runat="server">
    </telerik:RadScriptManager>
    <div style="padding-top: 8px; padding-left: 12px;">
        <telerik:RadButton ID="RadButton1" runat="server" Text="Instructions" BackColor="#282872"
            Width="100%" EnableEmbeddedSkins="true" Skin="Web20" Font-Size="10pt" Font-Names="verdana"
            Font-Bold="true" BorderWidth="0px" Height="30px">
        </telerik:RadButton>
        <div style="border: solid; border-color: #D7D7D7; background-color: #D7D7D7; margin-bottom: 2px;
            border-width: 1px 1px 1px 1px; line-height: 1.8em; width: 101%; height: 80%;
            font-family: Verdana; font-size: 1em; font-weight: normal;">
            <p style="padding-left: 5px; padding-top: 10px; font-size; padding-right: 5px; text-align: left;">
                *Fill in your personal <b>e-mail ID e.g. bob.smith@hotmail.com </b>and please note
                that all the test related communication will be sent to you on this email address.<br />
                <br />
                *Provide your <b>contact number</b> which can either be a mobile number or a landline
                number with area code.
                <br />
                <br />
                *Remember that <b>password</b> is case sensitive and it should be atleast six characters.
                In case you forget the password it will be sent to you at your email address.<br />
                <br />
                *On completion of this form you will be taken to <b>paypal website</b> for the payment
                and after the payment is complete you can start practising for the test.
                <br />
                <br />
                *Your browser must accept <b>cookies</b> in order to successfully register and sign-in.
                <br />
                <br />
                <a href="http://faq.external.bbc.co.uk/questions/bbc_online/cookies" target="_blank">
                    Learn how to enable cookies</a>
            </p>
        </div>
    </div>
</asp:Content>
<asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder2" runat="Server">

  <script type="text/javascript"  language="javascript">
      function UpdateImg(ctrl, imgsrc) {
          var img = document.getElementById(ctrl);
          img.src = imgsrc;
      }
    </script>

   
    <div style="height: 10px;">
    </div>
    <asp:Panel ID="pnlRegister" runat="server" Width="100%" Style="border: 1px; border-color: #D7D7D7;
        border-style: solid; padding: 5px; height: 600px;">
        <div style="height: 10px;">
        </div>
        <h1 style="margin-bottom: 3px;">
            Register</h1>
        <br />
        <div style="background-color: White;">
            <div class="GenericLabel">
                <asp:Label ID="Label22" runat="server" Text="Title"></asp:Label>
                <asp:Label ID="lblTitle" runat="server" Text="*" ForeColor="Red" Visible="false"
                    Font-Size="8pt" Font-Bold="true" Font-Names="verdana"></asp:Label>
            </div>
            <div class="GenericLabel" style="padding-bottom: 5px;">
                <asp:DropDownList ID="ddlTitle" runat="server" AutoPostBack="false" Width="250px">
                    <asp:ListItem Selected="True"></asp:ListItem>
                    <asp:ListItem>Mr</asp:ListItem>
                    <asp:ListItem>Mrs</asp:ListItem>
                    <asp:ListItem>Ms</asp:ListItem>
                    <asp:ListItem>Miss</asp:ListItem>
                    <asp:ListItem>Other</asp:ListItem>
                </asp:DropDownList>
            </div>
            <div style="height: 20px;">
            </div>
            <div class="GenericLabel">
                <asp:Label ID="Label1" runat="server" Text="First name"></asp:Label>
                <asp:Label ID="lblFirstname" runat="server" Text="*" ForeColor="Red" Visible="false"
                    Font-Size="8pt" Font-Bold="true" Font-Names="verdana"></asp:Label>
            </div>
            <div class="GenericLabel">
                <asp:TextBox ID="txtFirstname" runat="server" Width="250px"></asp:TextBox>
            </div>
            <div style="height: 20px;">
            </div>
            <div class="GenericLabel">
                <asp:Label ID="Label2" runat="server" Text="Surname"></asp:Label>
                <asp:Label ID="lblSurname" runat="server" Text="*" ForeColor="Red" Visible="false"
                    Font-Size="8pt" Font-Bold="true" Font-Names="verdana"></asp:Label>
            </div>
            <div class="GenericLabel">
                <asp:TextBox ID="txtSurname" runat="server" Width="250px"></asp:TextBox></div>
            <div style="height: 20px;">
            </div>
            <div class="GenericLabel">
                <asp:Label ID="Label11" runat="server" Text="Telephone no "></asp:Label>
                <asp:Label ID="lblContactNo" runat="server" Text="*" ForeColor="Red" Visible="false"
                    Font-Size="8pt" Font-Bold="true" Font-Names="verdana"></asp:Label>
            </div>
            <div class="GenericLabel">
                <asp:TextBox ID="txtTelephonenumber" runat="server" Width="250px"></asp:TextBox>
            </div>
            <div style="height: 20px;">
            </div>
            <div class="GenericLabel">
                <asp:Label ID="Label6" runat="server" Text="Email"></asp:Label>
                <asp:Label ID="lblEmail" runat="server" Text="*" ForeColor="Red" Visible="false"
                    Font-Size="8pt" Font-Bold="true" Font-Names="verdana"></asp:Label>
            </div>
            <div class="GenericLabel">
                <asp:TextBox ID="txtEmail" runat="server" Width="250px"></asp:TextBox>
            </div>
            <div style="height: 20px;">
            </div>
            <div class="GenericLabel">
                <asp:Label ID="Label8" runat="server" Text="Password"></asp:Label>
                <asp:Label ID="lblPassword" runat="server" Text="*" ForeColor="Red" Visible="false"
                    Font-Size="8pt" Font-Bold="true" Font-Names="verdana"></asp:Label>
            </div>
            <div class="GenericLabel">
                <asp:TextBox ID="txtPassword" runat="server" TextMode="Password" Width="250px"></asp:TextBox>
            </div>
            <div style="height: 20px;">
            </div>
            <div class="GenericLabel">
                <asp:Label ID="Label9" runat="server" Text="Confirm Password"></asp:Label>
                <asp:Label ID="lblConfirmPassword" runat="server" Text="*" ForeColor="Red" Visible="false"
                    Font-Size="8pt" Font-Bold="true" Font-Names="verdana"></asp:Label>
            </div>
            <div class="GenericLabel">
                <asp:TextBox ID="txtConfirmPassword" runat="server" TextMode="Password" Width="250px"></asp:TextBox>
            </div>
            <br />
            <br />
           
            <div runat="server" id="DivOutput" visible="false">
                 <asp:ImageButton ID="ImageAjax" runat="server" ImageUrl="~/Images/ajax-loader.gif"
                    AlternateText="Please wait" Visible="true" />
                <br />
                <asp:Label ID="lblOutput" runat="server" Text="" class="GenericLabel" ForeColor="Red"
                    Visible="true"></asp:Label>
                <br />
                <br />
            </div>
            <div class="GenericLabel" style="text-align: left;">
                <telerik:RadButton ID="btnSubmit" runat="server" Text="Subscribe" OnClick="btnSubmit_Click"
                    BackColor="#282872" Width="100px" EnableEmbeddedSkins="true" Font-Size="10pt"
                    Font-Names="verdana" Font-Bold="true" BorderWidth="1px" BorderColor="White" Height="30px">
                </telerik:RadButton>
                <br />
                <div style="height: 10px;">
                </div>
                <div class="GenericLabel">
                    <asp:Label ID="Label3" runat="server" Text="Subscription Package £6.99"></asp:Label>
                    <asp:Label ID="Label4" runat="server" Text="*" ForeColor="Red" Visible="false" Font-Size="8pt"
                        Font-Bold="true" Font-Names="verdana"></asp:Label>
                </div>
            </div>
        </div>
        <div style="height: 30px; float: right">
            <asp:Image ID="Image1" runat="server" ImageUrl="~/Images/paypalbuynow2.jpg.png" />
        </div>
    </asp:Panel>
    <div runat="server" id="ShowResult" visible="false">
        <h1 style="padding-top: 15px; margin-bottom: 5px;">
            Register</h1>
        <br />
        <br />
        <asp:Label ID="lblResult" runat="server" Text="" class="GenericLabel" ForeColor="Red"></asp:Label>
        <div class="GenericLabel" style="text-align: left;">
            <br />
            <telerik:RadButton ID="btnContinue" runat="server" Text="Continue" Font-Names="Verdana"
                OnClick="btnContinue_Click" Font-Size="10pt" ForeColor="#282872" Font-Bold="true"
                Width="100px" Skin="Default">
            </telerik:RadButton>
            <br />
            <br />
        </div>
    </div>
    <div style="height: 20px;">
    </div>
</asp:Content>

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using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Text.RegularExpressions;
using System.Text;
using Quiksoft.FreeSMTP;
using CustomForm;
using System.Collections;

public partial class PL_Register : System.Web.UI.Page
{
    protected void Page_PreInit(object sender, EventArgs e)
    {

    }


    protected void Page_Load(object sender, EventArgs e)
    {
        btnSubmit.Attributes.Add("onclick", "setTimeout(\"UpdateImg('ImageAjax','Images/ajax-loader.gif');\",50);");

        MaintainScrollPositionOnPostBack = true;
        
        ArrayList alCust = new ArrayList();
        Session.Add("CustList", alCust);


        if (!Page.IsPostBack)
        {
           
        }

    }
    protected void btnSubmit_Click(object sender, EventArgs e)
    {

        if (Validation())
        {
            string str= Guid.NewGuid().ToString();
            Customer obj = new Customer();
            obj.CustomerID =str.ToString();
            obj.Title = ddlTitle.SelectedItem.Text.ToString();
            obj.FirstName = txtFirstname.Text.ToString();
            obj.Surname = txtSurname.Text.ToString();
            obj.TelephoneNo = txtTelephonenumber.TemplateControl.ToString();
            obj.Email = txtEmail.Text.ToString();
            obj.Password = txtPassword.Text.ToString();


            ArrayList alCust = (ArrayList)Session["CustList"];
            alCust.Add(obj);
            Session.Add("CustList", alCust);

           
            Session["CustID"] = str.ToString();

            //Response.Redirect("~/Payment.aspx");

            DataClassesDataContext myContext = new DataClassesDataContext();


          
            var i = myContext.SP_InsertCustomer(str.ToString(), ddlTitle.SelectedItem.Text, txtFirstname.Text, txtSurname.Text, txtTelephonenumber.Text, txtEmail.Text, txtPassword.Text, string.Empty, System.DateTime.Now, System.DateTime.Now, "False");
            Response.Write(PayPalPostForm().ToString());
            this.PayPalPostScript(Page);
            DivOutput.Visible = true;
            lblOutput.Text = "Please wait you will be redirected to paypal website in few seconds...";
            ImageAjax.Visible = true;
            
          
            btnSubmit.Enabled = false;


            

         

            //    //ClearFields();
            //}
        }
        else
        {
            //lblOutput.Visible = true;

        }
    }

    protected void btnRedirect_Click(object sender, EventArgs e)
    {

        Response.Redirect("~/Login.aspx");
    }

    protected void btnContinue_Click(object sender, EventArgs e)
    {
        Response.Redirect("~/Payment.aspx");
        // Response.Redirect("~/Login.aspx");
    }

    protected void ClearFields()
    {



        ddlTitle.SelectedIndex = 0;
        txtFirstname.Text = "";
        txtSurname.Text = "";
      
        txtEmail.Text = "";
       
        txtTelephonenumber.Text = "";
        txtPassword.Text = "";
        txtConfirmPassword.Text = "";


    }



    protected bool Validation()
    {

        bool status = false;
        int count = 0, emailcount = 0;

        if (ddlTitle.SelectedItem.Text == "")
        {
            lblTitle.Visible = true;
            count++;
        }
        else
            lblTitle.Visible = false;


        if (txtFirstname.Text == "")
        {
            lblFirstname.Visible = true;
            count++;

        }
        else
            lblFirstname.Visible = false;


        if (txtSurname.Text == "")
        {
            lblSurname.Visible = true;
            count++;

        }
        else
            lblSurname.Visible = false;



        if (txtEmail.Text == "")
        {
            lblEmail.Visible = true;
            count++;

        }
        else
            lblEmail.Visible = false;


       

        if (txtTelephonenumber.Text == "")
        {
            lblContactNo.Visible = true;
            count++;

        }
        else
            lblContactNo.Visible = false;




        if (txtPassword.Text == "")
        {
            lblPassword.Visible = true;
            count++;

        }
        else
            lblPassword.Visible = false;

        if (txtConfirmPassword.Text == "")
        {
            lblConfirmPassword.Visible = true;
            count++;

        }
        else

            lblConfirmPassword.Visible = false;

        if (String.IsNullOrEmpty(txtEmail.Text))
        {
            lblEmail.Visible = true;
            count++;
        }
        else
        {

            lblEmail.Visible = false;
            if (isEmail(txtEmail.Text) == false)
            {
                lblEmail.Visible = true;
                count++;

            }

            if (CheckIfTheUserAlreadyExist())
            {
                lblEmail.Visible = true;
                //lblEmail.Text = "you are already registered using this emailID.";
                emailcount++;
            }
        }


        if (txtPassword.Text != txtConfirmPassword.Text)
        {
            status = false;
            count++;

        }

        if (count == 0 && emailcount == 0)
            return true;
        else
        {
            if (emailcount > 0)
            {

                DivOutput.Visible = true;
                lblOutput.Visible = true;
                lblOutput.Text = "You are already registered using this emailID";

                return false;

            }

            DivOutput.Visible = true;
            lblOutput.Visible = true;
            lblOutput.Text = "Please complete the fields marked with *";

            return false;


        }



    }


    public bool isEmail(string inputEmail)
    {
        if (inputEmail == null || inputEmail.Length == 0)
        {
            throw new ArgumentNullException("inputEmail");
        }

        const string expression = @"^([a-zA-Z0-9_\-\.]+)@((\[[0-9]{1,3}" +
                                  @"\.[0-9]{1,3}\.[0-9]{1,3}\.)|(([a-zA-Z0-9\-]+\" +
                                  @".)+))([a-zA-Z]{2,4}|[0-9]{1,3})(\]?)$";

        Regex regex = new Regex(expression);
        return regex.IsMatch(inputEmail);
    }

    protected bool CheckIfTheUserAlreadyExist()
    {

        DataClassesDataContext myContext = new DataClassesDataContext();

        var i = myContext.sp_CheckIfTheUserAlreadyExist(txtEmail.Text).ToString();

        int j = Int32.Parse(i);

        if (j > 0)
            return true;
        else
            return false;


    }



    protected void SendConfirmationEmail()
    {


        string MailFrom, MailTo, MailMsg, MailSub;

        MailFrom = "no-reply@practicelifeintheuktest.co.uk";
        MailTo = txtEmail.Text.ToString();
        MailSub = "Welcome to PracticeLifeInTheUKTest";
        MailMsg = "Dear" + ' ' + txtFirstname.Text.ToString() + ' ' + txtSurname.Text.ToString() + ",<br /><br /> Thank you for registering with www.practicelifeintheuktest.co.uk. <br /><Br />Your account has been activated. If you have any problems accessing your account then please contact us at <Br /> support@lifeintheuktest.co.uk <Br /> <Br />Thank you<br /><b>www.practicelifeintheuktest.co.uk Support Team</b><br />";


        //SMTP.QuickSend("ch.nes.scot.nhs.uk", MailTo, MailFrom, MailSub, MailMsg, BodyPartFormat.Plain);

        DT_SendEmail obj = new DT_SendEmail(MailTo, MailFrom, MailSub, MailMsg);
        obj.SendEmailWithOutCC();



    }

    public string PayPalPostForm()
    {
        //PayPal cart version
        string PostUrl = "https://www.sandbox.paypal.com/cgi-bin/webscr";
        string cmd = "_xclick";
        string business = "seller_1317425768_biz@hotmail.co.uk";
        string lc = "GB";
        string item_name = "PracticeLifeInTheUKTest.co.uk";
        string amount = "6.99";
        string currency_code = "GBP";

        string button_subtype = "services";

        string no_note = "0";

        string bn = "PP-BuyNowBF:btn_paynow_SM.gif:NonHostedGuest";


        string CustID = Session["CustID"].ToString();


       //Create the Form to write to the page with PayPal parameters
        StringBuilder ppForm = new StringBuilder();
        ppForm.Append("<Form name=" + "\"" + "frmPP" + "\"" + " id=" + "\"" + "frmPP" + "\"" + " action=" + "\"" + PostUrl + "\"" + " method=" + "\"" + "post" + "\"" + ">");
        ppForm.Append("<input type=" + "\"" + "hidden" + "\"" + " name=" + "\"" + "cmd" + "\"" + " value=" + "\"" + cmd + "\"" + ">");
        ppForm.Append("<input type=" + "\"" + "hidden" + "\"" + " name=" + "\"" + "business" + "\"" + " value=" + "\"" + business + "\"" + ">");
        ppForm.Append("<input type=" + "\"" + "hidden" + "\"" + " name=" + "\"" + "lc" + "\"" + " value=" + "\"" + lc + "\"" + ">");
        ppForm.Append("<input type=" + "\"" + "hidden" + "\"" + " name=" + "\"" + "item_name" + "\"" + " value=" + "\"" + item_name + "\"" + ">");
        ppForm.Append("<input type=" + "\"" + "hidden" + "\"" + " name=" + "\"" + "custom" + "\"" + " value=" + "\"" + CustID + "\"" + ">");
        ppForm.Append("<input type=" + "\"" + "hidden" + "\"" + " name=" + "\"" + "amount" + "\"" + " value=" + "\"" + amount + "\"" + ">");
        ppForm.Append("<input type=" + "\"" + "hidden" + "\"" + " name=" + "\"" + "currency_code" + "\"" + " value=" + "\"" + currency_code + "\"" + ">");
        ppForm.Append("<input type=" + "\"" + "hidden" + "\"" + " name=" + "\"" + "button_subtype" + "\"" + " value=" + "\"" + button_subtype + "\"" + ">");
        ppForm.Append("<input type=" + "\"" + "hidden" + "\"" + " name=" + "\"" + "no_note" + "\"" + " value=" + "\"" + no_note + "\"" + ">");
        ppForm.Append("<input type=" + "\"" + "hidden" + "\"" + " name=" + "\"" + "bn" + "\"" + " value=" + "\"" + bn + "\"" + ">");
        ppForm.Append("</Form>");

        return ppForm.ToString();
    }

    private void PayPalPostScript(System.Web.UI.Page Page)
    {
        //This registers Javascript to the page which is used to post the PayPal Form details
        StringBuilder strScript = new StringBuilder();
        strScript.Append("<script language='javascript'>");
        strScript.Append("var ctlForm = document.getElementById('frmPP');");
        strScript.Append("ctlForm.submit();");
        strScript.Append("</script>");
        Page.ClientScript.RegisterStartupScript(this.GetType(), "PPSubmit", strScript.ToString());
    }


   
}

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