Do you have a lot of edits to your tracks (punch ins, copy/paste etc.)? Sometimes the drive has to jump around to get to the edited data and that causes the drive busy error.
If that's the case, you can bounce the edited track to a new track so it's contiguous on your drive and that will eliminate the drive busy error. You may need to turn off the other tracks to do the bounce or else you'll just get the drive busy again.
Q: Is it good music? A: I Wish Art