I was about to post the same problem. I worked on a track for some time, and eventually got everything working beautifully, and when I made some tweak, a couple real tracks completely stopped working.

I tried the following: 1. Unmuted all instruments. That didn't work. 2. Regenerated all tracks. Nope. 3. Disabled and reenabled the non working tracks. 4. Swithced non working tracks over to midi and then reassigned real tracks... 5. Deleted midi data that was in that slot initially 6. Reset all bars... Nothing works. Very frustrating.

I have experienced this problem before, and can't remember whether I just started over or if the real tracks came back to life on their own.

Any help would be much appreciated. I assume a number of users are having this problem.