The usual reason a 1994 won't learn is that its learning memory is full.

Another possibility is that you have a really strange protocol that the UEI learning methods can't learn. That's rare and I've never heard of a Panasonic device using such a protocol.

Can you afford (time to reprogram setup codes and macros etc.) to delete everything in the 1994 with a 981 reset? Then you'd be sure learning memory wasn't full. If it still can't learn that signal, can it learn anything else? You should be able to determine whether the learning components are broken.

If you use JP1 and download the upgrade for the 1925, I expect someone in the JP1 group can figure out what to put in the 1994 to handle it without learning.