Delete duplicate registry key

I can’t delete a aparently duplicated key in the registry. I’ve tried launching a command with “at” command (for localsystem user permissions) and then regedit and regedt32, without success. It is not a permissions problem: I can’t change property nor permissions with regedt32. I can’t delete parent key, either.
RK’s reg.exe does not function.
System is W2000 server spanish with SP1.

Thanks in advance