asp.net - ModalPopupExtender OK Button click event not firing?

Question

I have a Button inside an UpdatePanel. The button is being used as the OK button for a ModalPopupExtender. For some reason, the button click event is not firing. Any ideas? Am I missing something?

<asp:updatepanel id="UpdatePanel1" runat="server">
    <ContentTemplate>
        <cc1:ModalPopupExtender ID="ModalDialog" runat="server" 
            TargetControlID="OpenDialogLinkButton"
            PopupControlID="ModalDialogPanel" OkControlID="ModalOKButton"
            BackgroundCssClass="ModalBackground">
        </cc1:ModalPopupExtender>
        <asp:Panel ID="ModalDialogPanel" CssClass="ModalPopup" runat="server">
            ...
            <asp:Button ID="ModalOKButton" runat="server" Text="OK" 
                        onclick="ModalOKButton_Click" />
        </asp:Panel>
    </ContentTemplate>
</asp:updatepanel>

Answer 1

Aspx

<ajax:ModalPopupExtender runat="server" ID="modalPop" 
            PopupControlID="pnlpopup" 
            TargetControlID="btnGo"
              BackgroundCssClass="modalBackground"
             DropShadow="true"
             CancelControlID="btnCancel" X="470" Y="300"   />


//Codebehind    
protected void OkButton_Clicked(object sender, EventArgs e)
    {

        modalPop.Hide();
        //Do something in codebehind
    }

And don't set the OK button as OkControlID.