Modal PopupExtender Fade Not Working

I have a basic modal popup extender that displays a gridview when I click on a link button from another gridview.
All my code is working but the fadein and fadeout.  When I click the linkbutton on the gridview the modal popup displays but doesn't fade in and when I click my close button it doesn't fade out.  
The fade works when I click on the panel itself so I am guessing I am specifying an incorrect object in my declaration but can't figure it out.
Code:
<asp:Panel ID="pnlPopup" runat="server" CssClass="modal" > <asp:Panel ID="pnlContent" runat="server" Width="930px"> <asp:Button ID="btnShowPopup" runat="server" style="display:none" /> <cc1:ModalPopupExtender ID="mdlPopup" ...