AuthDiag 1.0
It's out !! AuthDiag 1.0, which stands for Authentication and Access Control Diagnostics, the RC version was out there for quite a while, but I didn't really have time to test it, but it should be pretty similar to SSLDiag, which diagnose IIS SSL related issues. Both are MUST have tools, if you are administrating IIS servers.
From the download page...
AuthDiag 1.0 offers a robust tool that offers a efficient method for troubleshooting authentication on IIS 5.x and 6.0. It will analyze metabase configuration and system-wide policies and warn users of possible points of failure and guide them to resolving the problem. AuthDiag 1.0 also includes a robust monitoring tool called AuthMon designed at capturing a snapshot of the problem while it occurs in real-time. AuthMon is robust and specially designed for IIS servers removing any information not pertinent to the authentication or authorization process.