Apr 182007

After getting back from my honeymoon, I was immediately thrust onto a site which was suffering a serious error on the development server (Windows 2000, IIS5, Classic ASP). Every time a file in the ASP application was accessed an “Internal Error 500″ error would pop up as the Friendly Error Message, and “The system cannot find the file specified” as the “unfriendly” message. Allowing anonymous access to the site allowed the page to load, but the webapp wasn’t particularly useful without integrated security.

As it seemed to be a security setting, we turned off all permissions – still no luck. Looking through the log files, it was reporting as a HTTP error 401 (Unauthorised). After some more hunting, it was established that it was suberror 5, but IIS5 doesn’t easily report the suberror code for 401. Suberror 5 indicates that it was a custom ISAPI/CGI web application returning the error, and yes, there was a third party ISAPI component installed, by the name of UpFile. Disabling this ISAPI filter caused the problem to disappear.

I’m still not sure what the original problem was, but I’m leaning to a Windows hotfix installed on the development server breaking the component. As the problem hasn’t shown up in production, it’s still a mystery.

What was learned from this experience? First, it’s hard to find classic ASP information on the web, an impossible for this particular error, and secondly running a third party component from 2002 may not work in 2007 if anything changes on the machine (e.g., the operating system).

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