Logic Pro 9 - Suddenly no sound on certain tracks in certain places in the project!

I have a fairly large project up (aprox 70 tracks) and on the last chorus the hi hat track and lead vocal track is suddenly muted (nothing visual - the sound just disappears) then 2 seconds later pops back in, then the snare disappears for 1 second or so then pops back in. I tried to bounce the song and the artifacts was printed onto the bounce - Weird!



This song has deadline tomorrow, so please help!!

Logic Pro 9 - Suddenly no sound on certain tracks in certain places in the project!