Midi not playing when I hit play on MPC?

Hey folks, I have a slight problem that has me stumped. I will try to explain this quickly. When I try to record a softsynth with the MPC's sequencer, the softsynth will not play when I hit record, or play on the MPC. Although I can hear the softsynth fine when the MPC is not playing, or recording. I can see the midi signal, and even the meter level in Reaper though. Midi records fine within Reaper's sequencer still though. I am not sure what to try. Another really strange thing is that sometimes when I hit stop on the MPC it will trigger the softsynth sound! What is going on. ?

Any help is greatly appreciated.