I had an issue with some modules not working and the X10 people suggested that "it is possible that the module in question and your controller are on opposite phases of your house wiring." and to have some electrical work done to correct the problem or to move the transmitter to another outlet. The electric work would be costly and if I move to another outlet would I not be killing the working modules in favor of the non-working ones?
Anyway, I decided that since the RF remote control worked all the modules just fine and I have a few RF modules I would try send RF to turn on the lights. That works just fine, except there is an On and an Off macro for each. I assigned each a unused address (all 'on' macros are M and 'off' are L) with the # the same as the unit I was controlling. That has no function other than to keep the macros straight so I can tell which goes where.
Now if I could only understand why the Motion Sensor->Macro->Chime waits 60 seconds to chime I will be a happy camper.