It works fine if I press the button manually. It is hooked up to 2 incandescent lights. I verified the black is hooked up to line, and blue is on load.
Can you control it at all manually from within the software?
From what I have read it could be noise? but I haven't plugged in anything new since it stopped working. My shed is a little over 100 feet from the house and I never have any issues with that swith. My porch lights are probably only 30 feet from the panel. If it was a noise problem would I expect to see it on other modules too?
Noise can come from outside your house, too. (As many other members are singing along right now,) I had a noise problem last year that was created by a bad CFL bulb in the house across the street from mine. We are on the same transformer, and the noise was strong enough to make it across the street into my system and interfere with it.
Is your CM15A on the same phase as those lights, or the other phase? That can make a major difference with signal strength. YOU might not have changed anything, but you could have a CFL or standard florescent bulb that is going bad (that happened to me, too!), which is creating more noise than it did before.
One thing I noticed when I installed the switch, was that the codes were not set to the default A1 that the manual says it should come with. I'm wondering if this was somehow a return that someone else had a problem with.
It is entirely possible that it was a return, but then it should not have been sold as a new unit. X10 should replace it for you if it is defective.
I have also noticed a buzz sound from the switch when the lights are dimmed but I'm guessing that's normal?
Buzzing is actually normal for most dimmers (even the old manual kind). Most dimmers don't work by reducing the voltage going to the light. Here in the US (and Canada), our 110V power is a sine wave, alternating polarity between positive and negative at a rate of 60 cycles per second (60Hz). Most dimmers "chop out" part of that wave, turning the light off for part of the cycle. It happens so rapidy that your eyes and brain see the average, which is why the light looks dimmed. For example, dimming to 50% is really chopping out enough of the sine wave that the light is off for half of it. The buzzing that you hear is that rapid switching of the light.
I hope that makes sense.