I am aware that it is a well-known error. But the solutions available online are not working for me.
I have AJAX calendar extender inside an updatepanel. When I do postback, it is trying to create the AJAX extendar controls twice, hence the problem.
Solutions available are saying to set debug=false, which makes the error disappear but duplicate controls are created on the page. Each control is appearing twice.
What else I could try?
Thanks ARB
Finally, I got it solved by moving controls into a separate update panel.
I had both GridView and Ajax extender controls in one update panel. The postback is happening when I clicked on gridview row.
Now I have GridView in one update panel and other controls in another update panel. That fixed it.
Hope it saves somebody's invaluable time