a particular recording session shows dancing level meters but no output!

only this garageband project is behaving like this. i've opened other projects and listened to itunes and it all works. this particular project shows the level meters and compression lights and everything else as it's playing. each track shows it's producing sound. the master track is right in the middle as always. even the master track EQ analyzer shows something is playing. however, the level meter on the top right of the application is blank. it's turned up, but it's not showing a level. it's the only level meter/signal indicator light in the entire program that is NOT lit up. i cannot figure out where the problem is. i've restarted garageband, restarted my computer, saved the project as another name and re-opened it, etc. i'd open it in the old version of garageband but due to the AU's i've used, it would totally wreck the project. i suppose i could do it and have the AU's bypassed just to see if it plays, and then remix/remaster the whole thing. but i'd like to avoid that. any tips?