Ubermurf

MIDI notes onto a software instrument track on the Oxygen 25

Hey! I have an issue that has only just arisen in the last project I'm working on. Im using logic Pro X and an M-Audio Oxygen 25 midi keyboard. i have a section that is recorded with samples and a chord progression that i recorded using the M-Audio. I was in the process of recording a bass track on there M-Audio and the notes shifted up a semitone whilst playing live?? I tried to record it again by stepping down a semitone when playing live and it shifted again. I tried to record the bass line several times until it seem to work and the correct notes were playing back but when i pressed "Playback" the notes were wrong again?? i checked the piano roll and the notes are correct but just keep moving and changing. I can't seem to find a solution to this problem and I'm a bit of a techno-phone so if anyone has any solutions id be eternally grateful if you could explain in "Dumbass" (Me)terms. Thanks folks