Has a user’s name changed recently and they can no longer access a asp.net web application, or the information on the web application still reflects the old user name?
This could be because of the server caching the old username and not looking it up each time. To confirm whether this is what is happening you can disable the caching by doing the following.
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa
Create new DWORD labeled LsaLookupCacheMaxSize and set the value to 0
Reference: http://support.microsoft.com/kb/946358