While you are there pick yourself up a boosterlinc.
It may be a little pricy but it should help with your troubleshooting and maybe help solve your problem.
If ao does let you return the tester for credit, pick up another boosterlinc on the way back.
Smarthome recommends:
If the home is less than 2,000 sq. ft., start with a SignaLinc Plug-In Phase Coupler.
If the home is larger than 2,500 sq. ft., start with a SignaLinc Plug-In Coupler Repeater.
Install one BoosterLinc Plug-In Signal Booster for every 1,000 sq ft of living space in the parts of the house where you're having issues.
Install a FilterLinc Plug-In Noise Filter on each device that could be absorbing signals (TVs, A/V gear, computers, etc.).
The recommendation is sound, but take it with a grain of salt because they do have products they want to sell. From what I can tell, there's no harm in taking the advice as it only does good and not harm, but it will cost a pretty penny.
I currently have a PZZ01 with 2 boosterlinc setup. The PZZ01 just because of neighborhood paranoia. As far as filters, just grab a bunch of powerstrips from you local hardware with EMF/RFI with a lower boundry of 100kHz and make sure you plug all your regular electronic equipment into that (the higher the db rejection the better). X10 signals are at 120kHz. It does the job of the filterlinc's for me and saves a bundle.
www.automatedouted.com should have all the products from smarthome.
www.sensorsandmore.com has them in the X10 Tools section for a little lower, but not as wide a selection of other X10 stuff.
or go straight to the manufacturer
www.smarthome.com