I recently worked on a Windows 2003 server that required manual reboots in order to login, whether via console or Remote Desktop. After rebooting, Event ID 1517 was logged repeatedly in Event Viewer (protip: this error could also appear as Event ID 1524 in Windows Server 2003, or as Event 1000 in Windows Server 2000). Microsoft explains this error in better detail than I can in KB article 944984 - essentially, user profile registry hives are kept in limbo after log off, and never completely terminated. Unfortunately, the hotfix described in the KB article didn't help. I don't administrate this server, I was just called in to fix the issue without breaking anything else. At this point, I know the administrator had an application in need of some coding assistance. I didn't have time to review every application's authentication behavior, though, and I am a novice developer at best. As an alternative to reviewing miles of code, I installed the User Profile Hive Cleanup S