Trying to delete a stubborn registry entry, i finally found this solution:
It´s really powerful so must be used with a great amount of caution. It deleted the stubborn key instantly.
Under Administrator execution of the Command prompt, enter: psexec -s -i regedit
This will run regedit from the System account.
psexec can be found at: http://www.microsoft.com/technet/sysinternals/utilities/psexec.mspx
psexec’s normal use is to remotely interface other systems but it just happens to be able to run things like regedit from the System account.