It seems that occasionally, Windows Vista users can encounter a rather nasty bug which leaves them unable to log in to their system. If this is their only user profile, this can leave for a very distressing moment, particularly if the user is unfamiliar with Windows’ Safe Mode or various options available on the Vista DVD. The user is confronted with an error message such as the following:

The user profile service service failed the login. User profile cannot be loaded.

Or in German versions:

Die Anmeldung des Dienstes “Benutzerprofildienst” ist fehlgeschlagen. Das Benutzerprofil kann nicht gestartet werden.

From what I can gather, it appears that this problem occurs during Vista’s attempt to create a restore point. The user profile is backed up but no replacement is made. Thus these errors are most often seen after the installation of some new software or drivers, or after a Windows update, which may occur in the background with many users unaware of its activity.

Fortunately, some solutions are available, although not all appear to work in certain circumstances. Nigels blog offers a solution to restore the backup profile by editing the Windows registry. To do this, users need to:

1. Start the machine, and press F8 before Vista begins to load, choosing Safe Mode.
2. Search for the programme ‘regedit’ from the Start menu.
3. On opening this programme, navigate to HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindows NTCurrentVersionProfileList
4. Affected profiles can be located by the extension ‘.bak’. This extension should be deleted, the RefCount value should be 0, and the State value should be 0. Change accordingly and reboot the system.

German readers may also refer to this forum post.

Unfortunately this solution appears not to work in all cases. Since this problem generally appears to occur following a Windows Update or other software installation, however, it is equally possible to restore the system to a prior state and restore the working profile(s) to how they were before the incident. This might result in some strange behaviour or odd errors in some programmes, but these problems should only be minor ones. To do this

1. Start the machine in Safe Mode (hitting F8 before Vista loads, as above)
2. Search for the programme ‘rstrui’ in the Start menu.
3. On running the programme, the user should be presented with the option of restoring the system to the most recent restore point (recommended). Restore and restart.
4. Should the recommended option fail to solve the problem, follow the same procedure but use an older restore point. Hopefully one or other should do the trick.

Hopefully with the gradual rollout of Vista Service Pack 1, this type of problem will become less frequent.