Hi,
This almost certainly has to do with the code that dynamically load the ascx tab page. ASP.NET uses the full "path" to identify a control during post back and if one control is loaded at the same location in the control tree of another control, it could get the other control's view state data. When that happens, your controls will have an identify issue.
To resolve this issue, structure your controls tree in such a way so that this won't happen. For example, the following control tree can have problem:
Original Tree (-> means parent child relationship):
Post back Tree:
This can have problem because Y can get mixed up with X.
The following structure won't have problem:
Code:
A -> B -> C -> X
-> D
Post back:
Code:
A -> B -> C
-> D -> Y
Y in the second tree won't be mixed with X in the first tree.
Hope this helps.
Thanks!