We had active directory running 2000. There is a namespace in the 3.5 framework named System.DirectoryServices.AccountManagement. I used ContextType.Domain for the principalcontext and after performing serval user account tests, worked fine. Then the network administrator upgraded the domain to a new server and running server 2003 SP2. New using the ContextType.Domain the first ValidateCredentials attempt with a valid username and password returns false. Reexecute the same code immediately and the call returns true. Why is this happening after the upgrade?????? I tried the contexttype.machine and it returns the expected result of true. ContextType.Machine seems to be more reliable. To give more background information, using ASP.NET 3.5 with AJAX, XP client, 3.5 framework with SP1. The local guest account is disabled.
...
Go to the complete details ...