ASP.NET Ajax Error: Sys.WebForms.PageRequestManagerParserErrorException

Question

My website has been giving me intermittent errors when trying to perform any Ajax activities. The message I get is

Sys.WebForms.PageRequestManagerP         


        

Answer 1

I finally solved my variant of this same problem. I was attempting to copy/move a selected value between 2 listboxes in a webform. In my case, I had to specifically call {listbox}.ClearSelection() prior performing the action the 2nd time around.

So obviously this problem/error message can occur for a multitude of reasons.