Microsoft JScript runtime error: Sys.InvalidOperationException: Handler was not added through the Sys.UI.DomEvent.addHandler method.

Gentlemen,
Ladies,

I have an ajax tabcontainer on a webform. The webform always opens on a specific tab. Under certain circumstances the other 2 tabs are not enabled.

In that specific case I have a problem.

The idea is to have the user complete a form to complete their contactdetails. After it's been completed, the user is expected to click on OK. Visual Studio then throws the error "Microsoft JScript runtime error: Sys.InvalidOperationException: Handler was not added through the Sys.UI.DomEvent.addHandler method." It suffices to click on OK to have the user proceed.

After this everything works flawlessly: the details have been saved, and the other tabs are activated. Similar functionality on the other tabs does not have this problem. Any ideas?