What causes the 'Cannot unregister UpdatePanel' error?

Question

I\'ve got a UserControl that contains an UpdatePanel. When I put that on a page, it throws the following error:

Cannot unregister UpdatePanel with ID

Answer 1

This is a bit of a long shot, but I've had experiences with the AJAX extensions, specifically with the update panel, in which errors thrown by child controls were manifesting themselves as a different error thrown by the update panel. I did see a reference to this specific error being thrown due to an error in a child control:

http://msmvps.com/blogs/shareblog/archive/2009/03/11/cannot-unregister-updatepanel-with-id-since-it-was-not-registered-with-the-scriptmanager-and-moss.aspx

Not sure if this is the case for you or not, but I've spent many hours chasing down the wrong errors because of this.