I was still getting "Sys.WebForms.PageRequestManagerParserErrorException" error despite trying suggestions in the various website. To place a dummy session did not work as well as I had to put many variables into session and then redirect it to page i.e. I required to use Response.Redirect anyways (Server.Transfer did not work as well). The session variables had to be created after a button "btnFinish" was clicked. I tried following line of code
and actually it worked.