title: AJAX Toolkit Modal Popup won't appear
body: <p>I'm having some trouble calling a modal popup from server side.  So, I set the modalpopupextender's targetcontrolID to a hidden label.  Then in the codebehind from a button's click, I try to add this.modalpopup.show();  Unfortunately, the modal popup doesn't appear when this happens.  I can see the code get executed, but nothing shows.</p>
  
  <p>Here's my ASP.  minus the opening &lt; for the button and popupextender, because for some reason those lines won't display.</p>
  
  <pre><code>&lt;asp:Button CssClass="Button" ID="button" runat="server" Text="Button" AccessKey="m" meta:resourcekey="buttonResource1" OnClick="button_Click" /&gt; 
  
  &lt;ajaxToolkit:ModalPopupExtender ID="mpe" runat="server" TargetControlID="forpopup"
              PopupControlID="PopupPanel" BackgroundCssClass="modalBackground" /&gt;
  
         &lt;asp:Label ID="forpopup" runat="server" Visible="False"&gt;&lt;/asp:Label&gt;
  
          &lt;asp:panel id="PopupPanel" runat="server" BorderStyle="Groove" BorderColor="black" BorderWidth="3px" BackColor="AliceBlue" Height="200px" Width="200px" style="display: none"&gt;
  
              &lt;asp:Label ID="lblPopup" runat="server" Text="popup!"&gt;&lt;/asp:Label&gt;&lt;br /&gt;
              &lt;br /&gt;
              &lt;asp:DropDownList ID="ddlData" runat="server"&gt;
              &lt;/asp:DropDownList&gt;&lt;br /&gt;
              &lt;br /&gt;
  
              &lt;asp:Button ID="btnPopupOK" runat="server" Text="Ok" /&gt;
              &lt;asp:Button ID="btnPopupCancel" runat="server" Text="Cancel" /&gt;
          &lt;/asp:panel&gt;    
  </code></pre>
  
  <p>and here is my codebehind</p>
  
  <pre><code>    protected void button_Click(object sender, EventArgs e)
      {
          this.mpe.Show();
      }
  </code></pre>