I was getting this error when working with UpdatePanel, when I disabled few of the control inside updatepanel I was getting following error.
"sys.webforms.pagerequestmanagerservererrorexception : input string was not in correct format"...,
Looking around the world and some one suggested
1. Make ValidateRequest=false in the page directives
2. EnablePartialRendering = false
However, nothing worked for me. The problem was that I was trying to parse a blank value into in integer and that was causing the above bug.