It could be a permissions issue for asp
http://www.velocityreviews.com/forums/t75431-asp-error-when-uploaded-quotquotan-error-occurred-on-the-server-when-processing-the-urlquot.html
or parent path issues
http://dotnetwebprogramming.blogspot.com/2007/11/error-occurred-on-server-when.html
http://support.microsoft.com/kb/332117
Plenty more:
http://www.google.co.uk/search?q=An+error+occurred+on+the+server+when+processing+the+URL&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-GB:official&client=firefox-a