I have an ASP.NET application on a Windows Server 2003/IIS6 that refuses to run for some reason (it's the Xerox Centre, if that info helps). It has been working flawlessly before though on this server.

Now, all I get if I try to open the app homepage (http://some.intranet.server/XeroxCentreWareWeb/) is a "404 - File or directory not found" error.

• The app is configured to run in it's own app pool, which runs as Network Service.
• The Network Service account has read access to the configured directory.
• If I stop the app pool, I get the expected "Service Unavailable" message, meaning the app and its pool are wired correctly
• I tried to track down any file permission issues with procmon - nothing to be seen. There isn't even an access to the web app directory happening when the page loads.
• Interestingly, according to procmon, the web server accesses the 401-2 custom error file (Logon failed due to server configuration) first, but then decides to send the 404 down to the client.
• EDIT: The app runs with Windows-integrated authentication. Regular users have access to the app directory as well (I would have noticed file system "ACCESS DENIED" messages in procmon, if there had been any.)

This makes me think that there is some kind of weird permission problem that occurs even before the application files are being accessed. I just have no idea where to look.

I've tried to run the app pool as Local System for a test, but to no avail.

What else could I check in this case?