Our customer experienced multiple errors on a demonstration to a customer of theirs.
The site is asp.net 3.5 based and has been running pretty well lately. They said 2 hours later site was ok again... (needless to say they are not happy)
The traces in the health log look very weird, it appeared to be as if incomplete pages were returning to the server for processing..
A fair of of the errors were errors generated by scriptresource.axd with bits of the page source showing up as part of the url... very very odd. I'd never seen this before...
I was talking to their lead tester who then told me this only happened during a webex (cisco sharing product) demo and was fine after...
Is it possible the webex session could have impacted the site http stream between client and server...
This is a known IE8 issue. I bet you will see Trident/4.0 for all "broken" requests in the user agent field. (Google for "IE8 4K bug")
You can either run a different browser or appply the latest IE8 patch (this issue has already been fixed)