If a roaming profile cannot be loaded, the system looks for a local copy of the roaming profile.
If the local copy cannot be loaded, the system loads the default users profile, %Systemroot%\Documents and Settings\Default User.
When this happens, I prefer to log the user off. I also cause the system to delete the local copy of the roaming profile when the user logs offs.
You can implement these actions with group policy. Log users off when roaming profile fails and Delete cached copies of roaming profiles are both located at Computer Configuration\Administrative Templates\System\Logon.
If these policies are Not Configured, you can implement Log users off when roaming profile fails by using Regedt32 to navigate to:
On the Edit menu, Add Value name ProfileErrorAction, as a REG_DWORD data type, and set the data value to 1. When the profile server is unavailable, or there is an error, the user will be logged off.
You can implement Delete cached copies of roaming profiles, by using tip 0106:
Use Regedt32 to navigate to:
Edit or Add Value name DeleteRoamingCache, a REG_DWORD data type. Set the data value to 1.
NOTE: If you add ProfileErrorAction, you must also add it at:
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Group Policy Objects\LocalUser\Software\Policies\Microsoft\Windows\System