Parsing error from ASP.Net page when trying to execute javascript Alert

Greetings all

I am have a user control that sends an email. On successful send, I want to displaya message. I am using "Response.Write("<script>alert('Your email has been sent.')</script>");" but this gives me an error - "PageRequestManagerParserErrorException" (plse see attached jpg).

USerControl source and code-behind are attached.

What am I mising?

In advance, thanks!!

    allanmark

USER CONTROL SOURCE:
 
<%@ Control Language="C#" AutoEventWireup="true" CodeFile="MimeEmailer.ascx.cs" Inherits="UserControls_MimeEmailer" %>
 
<script type ="text/javascript" language="javascript">
 
 function ClearTheItXYZ()
{
   document.getElementById('<%=txtSubject.ClientID %>').value = '';
   document.getElementById('<%=txtMessage.ClientID %>').value = '';   
   var control = document.getElementById('<%=txtSubject.ClientID %>');
   if( control != null ){ control.focus(); }
   return false;
}
 
</script>      
 
<ajaxext:ScriptManagerProxy ID="ScriptManagerProxy1" runat="server">
</ajaxext:ScriptManagerProxy>
 
<ajaxext:UpdatePanel ID="UpdatePanelA" runat="server">
<ContentTemplate>
    <asp:Panel ID="pnlMail" runat="server" CssClass="pnlEMail" Width="600" BackColor="Lime">
    <br />
    
    <table id="email" style="position: relative" >
 
       <!-- To -->
       <tr>
            <td style="width: 75px">
                <asp:Label ID="lblTo" runat="server" CssClass="smallerFontSize">To:</asp:Label>
                </td>
                <td colspan="2">
                <asp:DropDownList ID="ddlAddresses" runat="server" Width="325px"></asp:DropDownList>                
            </td>
       </tr>      
       
        <tr>                
        <!-- Row: Blank  -->
            <td colspan="2" height="12"></td>
        </tr>
 
 
       <!-- Row: Subject -->
       <tr>                
            <td style="width: 75px">
		        <asp:Label ID="lblSubject" runat="server" CssClass="smallerFontSize" AssociatedControlID="txtSubject" Width="175px" >Subject:</asp:Label>
            </td>
            <td colspan="2">
                <asp:TextBox ID="txtSubject" runat="server" Width="350px"></asp:TextBox>
	    	    <asp:RequiredFieldValidator ID="rfvSubject" runat="server" CssClass="smallFontSize" ControlToValidate="txtSubject"
                    ErrorMessage="Required Field" SetFocusOnError="True" Style="position: relative" ValidationGroup="SendEmail"></asp:RequiredFieldValidator></td>            
    	<!-- End: Row: Subject -->
        </tr>
 
        <tr>                
        <!-- Row: Blank  -->
            <td colspan="2" height="12"></td>
        </tr>
            
        <tr>                
        <!-- Row: Message -->
            <td style="width: 75px">
    		    <asp:Label ID="lblMessage" runat="server" CssClass="smallerFontSize" AssociatedControlID="txtMessage">Message:</asp:Label>
            </td>
            <td colspan="2">
		        <asp:TextBox ID="txtMessage" runat="server" TextMode="MultiLine" Width="475px" Height="200px"></asp:TextBox>
		        <asp:RequiredFieldValidator ID="rfvMessage" runat="server" CssClass="smallFontSize" ControlToValidate="txtMessage"
                    ErrorMessage="Required Field" SetFocusOnError="True" Style="position: relative" ValidationGroup="SendEmail"></asp:RequiredFieldValidator>        
            </td>            
	    <!-- End: Row: Message -->
        </tr>
 
        <tr>                
	    <!-- Row: Blank  -->
            <td colspan="2" height="1"></td>
        </tr>
              
    <!-- End: table id="email". -->
    </table>     
    
    <center>
    <asp:Button ID="btnSendTheEMail" runat="server"  Text="Send" ValidationGroup="SendEmail" CssClass="buttons" OnClick="btnSendTheEMail_Click" />  
    &nbsp;&nbsp;&nbsp;
    <asp:Button ID="btnClear" runat="server" Text="Clear" OnClientClick="return ClearTheItXYZ()" CausesValidation="False" />        
    </center><br />
 
 
    </asp:Panel>
    <!-- <asp:Panel ID=pnlMail"> -->
 
</ContentTemplate>        
</ajaxext:UpdatePanel>
 
 
 
USER CONTROL CODE BEHIND:
 
using System;
using System.Data;
using System.Text;
using System.Configuration;
using System.Collections;
using System.Collections.Generic;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using DataTransferObjects;
using BusinessLogic;
 
 
public partial class UserControls_MimeEmailer : System.Web.UI.UserControl
{
 
    private List<EMailAddress> emailList = new List<EMailAddress>();
 
 
    protected void Page_Load(object sender, EventArgs e)
    {
        // Load the Page-specific stylesheet.
        //HtmlLink lnk = (HtmlLink)Master.FindControl("cssLink");
        HtmlLink lnk = new HtmlLink();
        lnk.Href = "~/CSS/UserControls.css";
 
        //        txtMessage.Attributes.Add("OnClientClick", "return false;");
 
        if (!Page.IsPostBack)
        {
            emailList = BusinessLogic.Business.GetEmailAddress();
            ddlAddresses.DataSource = emailList;
            ddlAddresses.DataTextField = "Name";
            ddlAddresses.DataValueField = "Email";
            ddlAddresses.DataBind();
 
            ddlAddresses.SelectedIndex = 0;
            Session["selectedEmail"] = ddlAddresses.SelectedIndex;
 
        }
        else
        {
            if (Session["selectedEmail"] != null)
            {
                ddlAddresses.SelectedIndex = (int)Session["selectedEmail"];
            }
            else
            {
                ddlAddresses.SelectedIndex = 0;
                Session["selectedEmail"] = ddlAddresses.SelectedIndex;
            }
        }
    }
 
 
    protected void btnSendTheEMail_Click(object sender, EventArgs e)
    {
        bool isEmailSent = BusinessLogic.Business.SendEmail(ddlAddresses.SelectedValue.ToString(),
                                                       System.Configuration.ConfigurationManager.AppSettings["AdminEmail"].ToString(),
                                                       txtSubject.Text,
                                                       txtMessage.Text + Environment.NewLine + Environment.NewLine);
        if (isEmailSent)
        {
 
            Response.Write("<script>alert('Your email has been sent.')</script>");
                  ClearTheFields();
        }
        else
        {
            //   Message to go here.     
        }
    }
 
    private void ClearTheFields()
    {
        ddlAddresses.SelectedIndex = 0;
        txtSubject.Text = "";
        txtMessage.Text = "";
        txtSubject.Focus();
    }
 
 
}

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Error.jpg