Profile unload failures at logoff
"Sometimes, earlier versions of Windows falied to unload the registry portion of the user profile. Many times this failure prevented the user from subsequent logons to the same computer. Windows Vista always unloads the registry portion of the user profile, even if it must forcefully do so, prior to synchronizing the profile to the profile server. Windows, when forcefully unloading profiles, writes an event message to the event log. The description of the event contains the name of the process that prevented the registry from unloading and the closed registry path."