sys.webforms.pagerequestmanagerparsererrorexception: The message received from the server could not be parsed. Common causes for this error are when the response is modified by calls to Response.write(), response filters, httpmodules, or server trace is enabled.
Details : Error parsing near ‘<!DOCTYPE html PUBLI’.
In my case I chose to examine the error condition, if there’s one the change the window.location and redirect the client to an error page. You can examine the args to see exactly what was returned to make more interesting decisions about how to process the error. Also you should mark the error has handled (=true) if you don’t want the UpdatePanel to carry on raising browser errors.