This often coincided with power line surges and sage, either from the mains or from local high-current equipment turning on or off. So, before spending a lot of time troubleshooting PLC problems consider replacing those ancient modules. Jeff also reports that, in his experience, Leviton Manufacturing Co, Inc. products experience fewer failures than X10 products. Most experts would agree, however, that products by either Leviton or X10 have far fewer failures than the obscure brands you pick up via catalogs, flea markets, and electronics shops. The cost difference between name and obscure brands is trivial compared with the time and effort of troubleshooting problems.
Fluorescent lights are a particular problem for professional installers.
Make sure that any surge suppressors and other devices you use are X10 compatible. You may need a whole house filter if there is another X10-enabled house in your neighborhood. In that case, you may notice lots of poltergeists. Rooks says a typical symptom is that, at 2 a.m., every light in your house spontaneously goes on. Most homes are wired in two distinct phases, or electrical loops.