System.InvalidOperationException: Stack empty

Question

Once running ASP.NET 4.x application built in Visual Studio 2013 I am getting the below exception.

I have tried to disable the PageInspector by removing page inspect

Answer 1

That Happend to me when I added a new to my page and set the DefaultButton to a button outside the panel (By mistake). Error fixed when I changed the DefaultButton to another one inside the panel.