Coincidentally, I'm having an issue with my RM as well. It will not turn on a zone, when the receiver has the antenna hooked in. When I remove it, it will receive the signal and turn a zone on and off as instructed by be pressing the button on the transmitter. When I hook the antenna back in, it will not turn any zones on or off.
Ideas? I haven't cleaned it off yet to see if it's some weird dirty contact issue.