If you plug the CM15a back in, and open up AHP, do you see it receiving commands?
What housecode are you using?
Here are a few things that I've seen cause similar behavior:
1) a remote (hand-held, keychain, etc) that is stuck somewhere, and the buttons are being pressed (under a couch cushion, behind a bed, under a pile of stuff on a table).
2) a motion sensor that has weak batteries.
3) a new neighbor that got X10, and it trying it out - that's why you want to look to see if the signals are being picked up by the CM15A, and what other signals (not on your housecode) you might see.
What types of modules do you currently have?
Are all of them misbehaving, or only some of them?
Are they all on the same housecode, or different housecodes?