Windows Vista/7 displays this error at logon:

Group Policy Client Service Failed the logon - Access Denied

The problem is that permissions *within* the registry (not the NTFS permissions
on the NTUSER.DAT file -- though check those too) are wrong. This usually
happens when you're trying to rename a user in a roundabout way because
Microsoft disabled the 'copy profile' function in Windows Vista/7... but that's
another rant.

To fix this, log on as administrator, run regedit, go to HKEY_USERS, File >
Load Hive, load the NTUSER.DAT file for the malfunctioning user account, then
go to permissions on that key. Make sure the user account's current name is in
there; if it isn't, add it.

This should give enough permissions to log on, since the vast majority of
registry keys are set to inherit permissions and have no special entries
themselves. To find the ones that *do* have special stuff, open the registry
editor again as the user (once you're logged in) and go to HKEY_CURRENT_USER,
then export the entire key. If you get any "access denied" errors, those are
the keys that have special permissions. Note their names and fix them from

CAREFUL! always remember to file > unload hive again before switching users. If
you don't, NTUSER.DAT will stay locked under the admin account and Windows will
crap its pants.