I have a CM15A with the exact same symptoms. My x10 has always worked well, and I have motion sensors in the basement so when someone is carrying a load of laundry down they don't have to try to hit light switches too. Lately tho, the motion sensors stopped working. I noticed in testing the the CM15A seemed to not be responding to the motion sensors. I even tried some new motion sensors but same thing - no response - nothing listed in activity log. Then I came across this post. so thought I'd try it. I put new batteries in the unit, and tried the motion sensor (CM15A still plugged in to AC power) - no response. I then unplugged the CM15A from AC power, running just on batteries, and now it is seeing the signals from the motion sensors just fine!!! Shows up in the activity logs and everything!!! As soon as I plug the CM15A back into the AC outlet it stops seeing signals from the motion sensors again.
Everything else works, it just doesn't want to receive signals from the motion sensors anymore. I can still control all lights from the PC software when plugged into the CM15A via USB.
I am trying to justify the cost of buying another $100 unit just for the motion sensors.... might just stick with this for now and see if anyone can come up with a fix?