This is a very simple system. Until yesterday, it consisted of six wall switch modules (five WS467s and one three-way PLW02). The most important modules from the standpoint of security are the two outdoor light modules. I replaced them yesterday with self-contained GE programmable digital switches, which seem to work fine. Interestingly, the remaining X10 modules now also seem to work, at least so far. Hard to tell if the system is fixed or is just in one of its sporadic working periods. I should note that the modules I replaced were recently replaced brand new WS467 wall switch units. So, at least for now, I have a working system for the outdoor lights, and the AHP CM15A-controlled indoor lights are working as well. By the way, I reviewed every piece of electrical equipment in the house and couldn't find anything that coincided with or could account for the on-again, off-again nature of my CM15A problems. If the indoor lights continue to function OK, then I guess the problem must have been with the modules controlling the outdoor lights (which are ordinary carriage lamps with incandescent halogen bulbs and have been there for years). I might replace one of the outdoor light modules and see what happens. In any event, I am very grateful for all the help and suggestions. Thank you all very much.