I don't know much about ProTools free but I think it is trying to play the MIDI data on an external MIDI source and not on the SoundManager synthesizer (which is what QT does). ProTools is basically an audio tool, for multitrack recording, mixing, effects, audio for video and that kind of work. For MIDI I would go with something like Cubase or Digital Performer (which also have very good audio tools inside) and external MIDI gear.