I recieve this error while trying to use nested update panels and in debug the error points to viewstate. Here is my setup:

 

Usercontrol A: this has an update panel containing some input fields and the ajax uploader

Usercontrol B: this has an update panel containing some input fields and a multiview with a view that contains an instance of A

 

If I take usercontrol A and place it on a test page, everything works fine. When I nest them as above and I make the view active, the first time the uploader works fine but all later views (changing to another view and then back again) I get the 'Object Expected' error.

 

If I remove the update panel from usercontrol B, then everything works fine, except I have a postback when changing views in my multiview, which is not desired.

 

Any thoughts?