unwanted notes in instrument tracks
 

can anyone help?......desperation is setting in. when using instrument tracks for no apparent reason when playing back, there are extraneous notes being played that obviously NOT been programed or played. There is no sign of these 'notes ' in the region, so its not a simple matter of deleting them with a quick click. it happened when using a Korg O1FW and D4/D5. Cant understand it...can anyone else? thanks for your help.
Mac G5 dual 2.7ghz OSX 10.4.3
2 gig ram
002r
Lacie 250g ext H/D
P.S. doesnt like playing Reason either, operating system holding off etc.