You may have power line signal problems.
Like noise makers, signal suckers or phase coupling.
Jeff at JV Digital Engineering has a great set of troubleshooting tutorials.
http://jvde.us/x10_troubleshooting.htmOne thing is the CM15A should not be on the same circuit as the computing equipment, UPS AC Inputs or filtered surge suppressors to name a few.
With out a X10 signal type filter to isolate the equipment from the CM15A directly on the AC feed.
The HD243 is a unique X10 module running on both power lines for 220 volt operation. Most are 120 volts. So in this case the X10 power line signal has to be on both incoming lines. So I would say phase coupling wound have to get the power line command to both power lines feeding the HD243.
I am sure others will chime in and have more thoughts and recommendations.
There are Linux based X10 programs but the CM15A is not fully implemented in some of them. Like storing timers in it and then turning off the computer. To run standalone.
You may want to look here as a start.
http://www.linuxha.com/index.htmlhttp://www.heyu.org/