This is an issue for me. Since the week of 4Jan2010 I have been getting user reports that occasionally they see a javascript dialog saying...

Sys.WebForms.PageRequestManagerServerErrorException: An unknown error occurred while processing the request on the server. The status code returned from the server was: 500

...I have seen it myself. Clicking OK makes it go away and it does not appear to interfere with the operation of the site. It happens on here - www.oilconsolidation.co.uk (running 05.02.00 (275) upgraded about 18Dec2009) and it also happens here www.dynamisys.co.uk (running 04.09.04 upgraded 14May2009) both these sites are on the same server, they are different installations of DNN.

I don't believe I made any configuration changes or upgrades around 4Jan although I do allow the server (Windows 2003) to accept ALL windows updates. The problem could have been there before that date, that was when I got reports of it.

Googling suggests that this is AJAX related, but originally caused by an exception in the underlying page code. I had one user email me this morning. I can only assume he sent the email immediately after seeing the error (he included a screen shot of the dialog). There are no events in the event log since the application started message four hours earlier. This user was on the site home page. The home page has several Text/HTML modules, the What’s New module, and the News Feeds module. None of these has been upgraded on the site recently.

Anyone got any ideas to correct this problem?