It turns out that the Spektrum 2.4 module to convert the Multiplex Royal Evo 12 Radio needs a little modification before the radio will actually work. You must put a jumper on the main connector (white in the photo) between terminal #2 and #5

Once this jumper is installed, everything works perfectly. I talked to Horizon today and they didn’t know about it or that there was a problem. Now it’s solved.

[Update 1/27/10] This is only a problem if you have the Royal Evo Pro version of the radio and you will still need to ensure the software version is 2.62 or below. Multiplex has taken steps to block the PPM signal to disable 3rd party modules requiring direct PPM input.