Debugging authorization problems on IIS

A quote from Microsoft site:

Authentication and authorization failures are common on Internet Information Services (IIS) platforms. AuthDiag is a tool designed to aid customers in effectively troubleshooting and determining the root cause of the problem.

Here is a link to the facilitating debugging of the annoying 401 HTTP error!

http://www.microsoft.com/downloads/details.aspx?FamilyID=e90fe777-4a21-4066-bd22-b931f7572e9a&DisplayLang=en