Disappearing instrument sounds--help!


New Member
I am a rank amateur user of Logic Pro and Mainstage 2. I have a two-year-old MacBook Pro with plenty of RAM, etc. and an Axiom 61 controller keyboard.
As I am playing through my sets, I sometimes lose the sound of instruments. It seems to be connected with touching the mod wheel. Have communicated with the manufacturers of my instrument libraries and the M-Audio tech people. Each blames the other! Is there anyone out there who has some ideas? I would be very grateful!