I posted the below link in the wrong place, it belongs in this forum...

http://forums.asp.net/thread/1443129.aspx

This does seem to be a bug with the popup control.  Here is an abbreviated version of the code:

 <asp:UpdatePanel id="FormListEntry" runat="server">
        <ContentTemplate>
            

            <asp:LinkButton ID="AddListValue" runat="server" Text="Add List Value" onclientclick="return false;" /                            
       
            "AddPopupControl" runat="server" CssClass="modalPopup">
               <uc1:listValue id="AddListValueControl" runat="server" />
               <asp:Button id="AddListValueBtn" runat="server" text="Add List Value" OnClick="AddListValueBtn_Click" />
            </asp:Panel>
            
            <ajaxToolkit:PopupControlExtender runat="server" ID="testPopup" PopupControlID="AddPopupControl" TargetControlID="AddListValue" Position="right"  />
       </ContentTemplate>
    </asp:UpdatePanel>
 And the codebehind:
  
protected void AddListValueBtn_Click(object sender, EventArgs e)
        {   
            // this event is not getting raised

        }
  
Am I doing something wrong?
 

<asp:LinkButton ID="AddListValue" runat="server" Text="Add List Value" onclientclick="return false;" /> 
            <asp:Panel id="AddPopupControl" runat="server" CssClass="modalPopup">
               some content here
               <asp:Button id="AddListValueBtn" runat="server" text="Add List Value" OnClick="AddListValueBtn_Click" />
            </asp:Panel>

 
<ajaxToolkit:PopupControlExtender runat="server" ID="testPopup" PopupControlID="AddPopupControl" TargetControlID="AddListValue" Position="right"  />
 

jiffy:

This is still an issue -- it works properly in the modal popup, but does not work in the PopupControl.  Any ideas?

I have no idea how I came up with this, but try putting this in your page_load function:

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        Me.AddListValueBtn.UseSubmitBehavior = False
    End Sub

The click handler function is then reachable.  Actually, I think I had a similar problem and this came up, so maybe I do know where it came from.  

Let me know if this helped! 

Strange, but it did work.  Thanks :)