I'd try a couple of things
1) have a basic ASP page that doesn't do any logic except that could write out the date
2) Enable FRT (failed request tracing)
http://learn.iis.net/page.aspx/266/troubleshooting-failed-requests-using-tracing-in-iis-7/
3) Look in the httperror logs
%systemroot%\system32\logfiles\httperr and see if anything is there.
For more detail follow this link=
http://forums.iis.net/p/1174337/1966034.aspx