Losing boom sound.

Maybe this has been addressed but couldn't find it. I've been having Boom weirdness. I set up the inst track, get my pattern and midi data printed, all good, works fine for a few playbacks, then I lose audio. Midi data is still visible, I've tried opening boom, hitting play button there, still nada. If I delete and reconstruct the track it works again---for a few passes, then the same thing happens. Any ideas?
Pro Tools !0.3.5, Mac OS 10.6.8