Error on the page Event validation is enabled using <pages enableEventValidation="true"/> ?

Can someone help me with this? Please
I have a dropdownlist in my program.when I choose some of it's attributes I recieve this error:
Invalid postback or callback argument.  Event validation is enabled using <pages enableEventValidation="true"/> in configuration or <%@ Page EnableEventValidation="true" %> in a page.  For security purposes, this feature verifies that arguments to postback or callback events originate from the server control that originally rendered them.  If the data is valid and expected, use the ClientScriptManager.RegisterForEventValidation method in order to register the postback or callback data for validation.
what should I do? and what is this error for?

 

public partial class UserControls_publication : System.Web.UI.UserControl

    {

        private void Page_Load(object sender, EventArgs e)

        {

 

        }

 

        public void Search_Btn_Click(Object o, EventArgs e)

        {

            Page.Response.Redirect("ProjectDescCurrent.aspx?PID=" + ddlSearch.SelectedItem.Value);

        }

 

  }