I have a pair of Chamberlain Liftmaster Professional openers (Chamerlain Model 2500 belt drive) in my two-car garage. Both systems are identical, so it is easy to troubleshoot. I am able to completely program the right side with the security+ technology (easy, easy), but the left wasn't working...until the lights went out... Several days ago, the left side started working only intermittently. It would open just fine, but you'd have to use the inside push button to close it. And once it was closed, the remote stopped working until you tried again several hours later. Basically, it would work once, then stop for a while. I tried reprogramming both systems on each side. The right side, no problem. The left side wouldn't take any programmin until the lights on the opener went out (automatically about 1 minute after the last use). If I turn off the lights manually with the pushbutton control switch on the wall, I can program and operate it just fine. But if the lights are on (as is the case automatically when it is activated), the opener stops receiving signals. As soon as the lights go off (in a minute or so) automatically -- or as soon as I turn them off automatically, the remotes work fine. So basically, we can open the garage, back the car out, walk into the garage, turn off the opener lights manually, get back in the car and the remote will work. That is, as long as you done break the anti-crush security beam 6" from the ground, because if you do, the lights come on and the remote won't work. Odd... Coming home is no problem. The light is off so the remote works fine. But you have to close the door with the pushbutton switch once you get out of the car (unless of course, you get out, turn off the lights, then get back in the car to use the remote). This is the most bizarre problem I have ever encountered with an opener. I can find NOTHING on any of the internet blogs even remotely familiar. Before I call someone locally, who I doubt has ever seen then and just wants to sell me a new opener, I would be deeply grateful for any expert out there who thinks they know the answer here.