Out of curiosity, how old is your MX-500? I know there was an issue with *original* MX-500s with learning certain long codes on the LCD buttons (they supported fewer bits than the non-LCD buttons). In the end URC removed the ability to reset the remote to the factory default configuration, and used that memory for the LCD keys.

After a search I found another report of this issue (with the same keys in fact) but another poster said they were able to do it by changing their learning technique.

So I suggest trying out some of the tricks here: [Link: remotecentral.com]