Thursday, April 17, 2014

Intermittent PageRequestManagerParserErrorException With Full Postback

I have a project with a bunch of ajaxified Telerik controls within several nested UpdatePanel controls. As part of an Excel export process, I have a button which upon clicking performs a full postback, generates a spreadsheet from a RadGrid, and finally prompts the user to download the file. 

Once in a while, though, the export process would throw the dreaded and unhelpful Sys.WebForms.PageRequestManagerParserErrorException exception.

Eilon Lipton's helpful post gave a handy checklist of things not to do, but in spite of ensuring all the common causes were accounted for, it would still occur occasionally.

I tried implementing a workaround shared by a colleague and thus far it appears to have helped. This involves setting the OnClientClicked event handler of the export button so that it triggers a brief pause prior to initiating the full postback using a client-side Javascript.
function onExportClick(sender, args)

          function () 
               __doPostBack(, "_MyButtonID") 

The error itself points you in the right direction, but some more context sure would be nice. Anyway, apparently this script mitigates situations where the Telerik controls are still in the process of being rendered when the full postback is initiated, corrupting the Response header in the process.