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://technet.microsoft.com/en-us/sysinternals/bb897553.aspx
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.
Disclaimer: If you don’t know how to do this, should you really be poking around in the registry with full access rights? If you think so, look at this post for step by step instructions: