Batboard

I have a UHF MTS2000 that I cannot get MPL to work on. The firmware is 5.60. This radio is flashed for 250ch. I have a list of MPL's defined in CPS, I have a few personalities with MPL enabled.. I have the middle side button set for MPL.. Am I missing something? The radio totally ignores the side button.. Is there something else I have to adjust?

firmware dependent IIRC it has to be 6.xx or higher for MPL to work.