Well craig-o since the remotes work outside the room that kinda tells us that AHP is setup correctly to transceive the right house code. You might want to try and unplug the CM15A and plug it into an outlet in the room and try the remote.
First thing that comes to mind might be that the walls have a metal lath on them. Also could it be its built with metal studs? Either of these could interfear with the RF transmitting out of the room.
The other thing to watch for in bedrooms in newer houses being built, is the National Electric Code requires ARC Fault circuit breakers be installed. The local code may require other rooms to have them as well. This could mess up the PLC but shouldn't effect the RF.
(http://www.bdshost.com/X10/lpup.gif)---(http://www.bdshost.com/X10/lpup.gif)---(http://www.bdshost.com/X10/lpup.gif)---(http://www.bdshost.com/X10/lpup.gif)---(http://www.bdshost.com/X10/lpup.gif)----KDR
Another thought which helped me fill a couple of bad spots was to change the angle of the CM15A's antenna. Have you tried it in the horizontal position. This has helped others in the past. Also did you try relocating the CM15A in that room yet, just for a test?
(http://www.bdshost.com/X10/lpup.gif)---(http://www.bdshost.com/X10/lpup.gif)---(http://www.bdshost.com/X10/lpup.gif)---(http://www.bdshost.com/X10/lpup.gif)---(http://www.bdshost.com/X10/lpup.gif)----KDR