I have a website that has been using the ModalPopupExtender for a very long time. I recently added a TabContainer and started having problems with the ModalPopupExtender. Events in my popup stopped firing. I commented out the TabContainer code and the popup works correctly. To clarify, both ModalPopupExtender and TabContainer reside on the same page but I am not using one inside the other. I updated my AjaxControlToolkit to the latest version but it did not help. I am running .NET 4.0.
Does anyone have any suggestions?