Thursday, July 26, 2007

An intermittent PageRequestManagerParserErrorException

I was trying to make a site using a TabContainer and an UpdatePanel and I kept receiving a PageRequestManagerParserErrorException, but only sometimes. A page refresh would fix it and the message looked like "Error parsing near '<html>


'". The funny thing is that in the Ajax response output I had no <html> or <head>.
Trying desperately a fix detailed in this very nice post: Sys.WebForms.PageRequestManagerParserErrorException - what it is and how to avoid it , mainly forcing the start of a Session when the Page is first loaded, seemed to fix it. (put a if (!IsPostBack) Session["Siderite"]="rules"; in Page_Load)

So beware: the dreaded PageRequestManagerParserErrorException doesn't appear only when the response output is malformed, but apparently also when in some cases someone tries to start a Session from within an async postback.

If you have some other problem linked to this exception, read this post: ASP.Net Ajax and Response.Write or response filters The message received from the server could not be parsed.