Sometime these remotes get strange things in their memory and various things don't work until you do a 981 reset. It's fairly rare. I don't know how to confirm that it happened. I'm not sure it could explain the 979 command failing.

If you don't have too much already programmed in, try the 981 reset and see if 975 and 797 work after that. (After the 981 reset, you must re select your setup codes and re enter and macros or key moves you need).