Midi Input Trouble

Keyboard: Yamaha MO8 Synthesizer, with latest MIDI driver installed
Operating System: Mac OS X 10.8

I used PortMidi to test my Midi Keyboard and it works. Then, I when I tried to enter the notes in Note Entry Mode only three bass notes would show up and stop. MuseScore won't show anything after that.

I set my input device as USB 2.0 Yamaha MIDI on MuseScore (which was also used to test PortMidi). How come in Port-Midi, the my Yamaha worked fine, but in Musescore it didn't? I'm using a brand new MIDI-USB cable (and plugged IN to the MIDI-Out, and OUT to MIDI-in), but don't know the brand.