Thanks for the all the replies and great suggestions. I just finished some more troubleshooting and have more details and conclusions, as follows:
* The electric run tied to this breaker goes to two rooms (computer & exercise rooms,) so I thought. At least, that's what the label on the circuit panel said
* It turned out that the run was used to wire the downstairs laundry room where the washer was plugged in
* Unplugging everything on the same run allows me to get to the AM486 from my AHP machine w/out a problem
* Started adding devices one by one starting with the washer. wham.. X10 signal gone!
* Added an AF120 filter to the washer - all cool again
* Plugged in my high end Dell computer in computer room - signal gone
* Added an XPPF to the computer - still no signal
* Unplugged the computer and left ONLY the XPPF plugged in - still no signal
* Removed the XPPF - all cool again
* Tried all the XPPFs that I have, with nothing on them - no signal
* Moved to the next outlet and plugged in my laptop, print-server, and laser printer (off) with XPPF - no signal
* Tried all XPPFs - no signal
* Left outlet alone - all cool again
* Moved to the other room (exercise) and connected small 15" TV with XPPF - no signal
* unplugged TV and XPPF - all cool again
* plugged in treadmill - still cool. Turned on treadmill - still alright. unplugged treadmill.
* moved AM486 to different outlets around both rooms and tried plugging in stuff again as above - same results
* went back to Dell computer and laptop outlets and tried an AF120 instead of XPPFs - no signal
* left AF120 alone with nothing plugged in - no signal
Decided to use maxi-controller in the same room as the AHP machine instead of AHP
* turned AM486 on/off from maxi controller with only washer/AF120 on the run - no problem
* plugged in high end Dell computer w/out XPPF - no signal from maxi-controller
* added XPPF to Dell computer - all cool again
* turned on dell computer - still cool
* Plugged in laptop, print-server, and laser printer (all on) on power strip with XPPF - no problem
* Removed XPPF from power strip leaving laptop, print-server, and laser printer on - no signal
* moved to next room and plugged in 15" TV w/o XPPF - no signal
* added XPPF to TV - all cool
As of now, I have the CM15a on the second outlet, so I decided to connect it to the same outlet where the maxi-controller was (using a 25' 12-gage extension cord)
* Leaving everything as is (all devices running with XPPFs on them) - all cool. I can control everything from the AHP machine
So, I've concluded the following:
* I had two major problems:
1) the washer was the main source of noise that the XPPFs couldn't filter out. Adding the AF120 helped. Jeff gets the brownie points for this one!
2) my CM15a signal was too weak to reach all of that room after adding at least one other filter. It seems that each filter was making the signal weaker. Bill (wgjohns) gets the brownie for this one. He suggested I move the CM15a as close to the first outlet (closest to the breaker) as possible
* I've decided to move my CM15a to the new outlet - most likely by using a USB extender since it would be very inconvenient to have the AHP machine where that outlet is
* My XPPFs seem to be doing their job, albeit less than what I had expected, but working nevertheless
to all!