I recently experienced a confusing, head-ache-causing problem while deploying an MVC application to a Windows Server 2008.
The issue looked simple enough: the Web server returned a 401 (unauthorized) error when I tried to access the application, which required Forms Authentication to function properly.
Analyzing the issue
I started out with the basics. Check the anonymous and forms authentication settings, check the AppPool configuration, check if the AppPool user has all necessary rights, etc.
But all to no real avail. IIS kept redirecting me to the logon page (even when the session was authenticated!). Using fiddler it became more and