It's that the MX-500 cannot learn the commands from the newer equipment. It has something to do with the type of signal being sent (toggle bit codes?). I was never able to get my Philips TV, Motorola Cable box/PVR or the SMS-1 able to learn all commands into the MX-500. But I can say that I was able to send my 500 back to UEI and they programmed support for those earlier devices into my 500 for free. I only had to pay for the shipping to, they paid the rest. I think that's pretty good support. I DL'd the software for the 700 and found all of my devices, except the SMS-1, already in the data base. So it should be an easy upgrade.