error while trying to synchronize audio and midi

While recording a midi instrument horrible static occurs when the track reaches an audio track. It starts on the guitar track, but gets much worse when it reaches the vocal track (recorded with a Blue Snowball mic), slows down, then stops with the error message: "Error while trying to synchronize audio and midi. Sample rate 42690 recognized. Check conflict between garageband and external device." Some midi sounds are worse than others. Keyboards seem to be the worst.

Running Garageband 10.02

OS Maverick 10.9.2 on a Macbook Air.

A recording tech at Guitar Center suggested adjusting the amount of power garageband draws from the computer, but I don't have a clue how to do this.

No other apps are running in the background. I've tried just about all the settings in garageband and audio midi setup in the computer that I know of, but the problem persists and has rendered garageband unusable for midi instruments.

Possible solution: New mic and/or new guitar interface? Don't want to spend the $$$ unless I have to.