Thanks for the suggestions. Unplugging all of the computers didn't seem to help. I guess I should check for a bad switch before doing anything more complicated - hopefully that will take care of it.
The house is pretty small, about 1000 sq. ft. I did think about an amplified coupler, but as I said, I'm renting (hopefully buying this spring), the house and wiring are pretty old, and I don't want to spend a lot of money or effort. While I do feel comfortable wiring wall switches myself, I'm not as keen on venturing into the breaker box. Plus, it's expensive - I want to make sure that I really like X10 before I spend that kind of cash.
The main thing that made me think it wasn't the switch was that the activehome controller could control it when plugged into that one outlet. Maybe the switch just needs a stronger signal than it should or something...
My other controller is an RF remote; the transciever is on a different breaker but as I said, it has no problems controlling anything else including A7 which is on the same breaker as A8. I can also move the transciever around to see if it works.
