Sys.Webforms.PageRequestManagerServerErrorException: Cannot find table 0.

Hi everybody,
I prepared my code in a test page in order to try something that was new for me (gridview + updatepanel): the test was positive and everything was working.
As soon as I copied the code into my project... problems started to happen!!!
Now explorer is giving me this error when I press the update button:
Line: 4724
Char: 21
Error: Sys.Webforms.PageRequestManagerServerErrorException: Cannot find table 0.
Code: 0
URL: http://x.x.x.x/mypage.aspx?ref=wandetail
I made a search in google and it seems I'm the only one in the world that had the luck to try the version "cannot find table 0" of this error.
How can I solve it?
My page is quite particular, the layout it's similar to the one that follows:
<form id="frmAdmMod" runat="server"> <% Select Case Request.QueryString("ref ...