Delete a key from registry - Permission denied issue

get psexec is available from Microsoft here

http://technet.microsoft.com/en-us/sysinternals/bb897553.aspx

And then go to the folder of psexec and run following command. 

psexec -i -d -s c:\windows\regedit.exe

It will open regedit. then set the permisison in there and then you can delete.