Ran in to this one today spent an hour or two googling and proding for the answer. Essentially you are getting this message because the owner of the key is not you and has denied permission or has not given permission to you. The fix is very simple and should be obvious to those of you familiar with the NTFS file permission scheme. Just right click on the key above go to advanced reset the owner permission on child objects click ok (you may still get an error however) this will grant you control to the child element from above. From there you should be able to delete/modify the key normally.
