I had the same issue recently with the MX3000. It wouldn't learn certain codes. I tried everything. Finally I tried learnig the codes that wouldn't take into an old Marantz RC5000i. Voila, no problem. I then tried learning those newly learned codes from the RC5000i into the MX3000. It worked like a charm. I wonder if the URC remotes have a kind of code filter that rejects certain information that is percieved somehow as unaceptable. Or, that the RC50001 has a process that cleans up the codes. I'm not looking a gift horse in the mouth here, but I'm curious to know what's going on in this convoluted process.