Wow, I've been away for a while, and saw this pile of responses to my original post! I've tested this thing six ways to Sunday, on a clean circuit, everything else unplugged, no CFL's in my house. It's definitely the unit. The odd thing is sometimes it locks up, other times it jumps to the high order adresses (13-16). If no other transmitters are on the circuit, then what could cause that but a faulty unit? Beats me. I hope Bill will allow me to try one more (he's been absolutely great about this - both units are on the way back Bill!). If the third doesn't work, I'll have to look for some anomoly in the wiring. Unfortunately, the Pronto that I got my wife for Christmas is still sitting on my desk waiting for the X10 interface so I can control my no-discrete Toshiba gear!!!!!!