I recently added a post to our Support team blog which talks about unexpected 401.1 that you might see when you browse to an IIS 7.5 website over Windows Integrated Authentication. If you are seeing the following in the Error summary on your web page go check this link out.

Module WindowsAuthenticationModule
Notification AuthenticateRequest
Handler StaticFile
Error Code 0x80090305

Cheers to life!

Just in case if anyone bothers to track my blog here is an update. I have contributed two posts recently to our IIS/ASP.Net Support blogging site.

1. If you are seeing the following error during the IIS 6.0 Install/Setup:

Error writing encrypted data to the Web Server's configuration database (Metabase).

0x80090010=Access denied.

This post may be useful to you.

http://blogs.msdn.com/webtopics/archive/2010/04/26/iis-6-0-installation-setup-failure-with-the-error-0x80090010-access-denied.aspx

2. We had an article on http://learn.iis.net around how you can configure One-to-One mapping for client certificate authentication feature in IIS 7/7.5 but we did not have an equivalent for Many-to-One mapping. If you are interested you may want to follow the link below:

http://blogs.msdn.com/webtopics/archive/2010/04/27/configuring-many-to-one-client-certificate-mappings-for-iis-7-7-5.aspx

This post also highlights how you can use the cool Configuration Editor extension to manage IIS configurations including Client Certificate mapping and how easily and automatically you can generate code/scripts/commands to manage IIS features.