Hi - If it's only some audio files in the project that go missing, they may be corrupted, or the Project file itself may be corrupted. It sounds like it only happens with some recordings, which naturally makes it harder to pinpoint. I guess keep troubleshooting as you have been -- try to determine if it happens in multiple GB Projects (including new Projects) or only in one particular Project (which could indicate potential corruption of that Project). Note: The actual audio files (the .wavs) are stored inside the GarageBand Project file, which is really a package (a folder disguised as a file) -- if you right-click on it, choose Show Package Contents, and open Media, you should be able to see if the supposedly missing files are actually in there or if they are in fact missing. (Btw, the green or yellow Drum sequences you create in GB don't involve audio files, just MIDI data which is part of the Project file itself). Apple would probably advise you to reinstall GarageBand, which I guess couldn't hurt. Of course an issue like this could also be part of a hard disk issue -- make sure your hard disk is not too full, the startup disk should always be at least 20% empty to avoid slowdowns and potential file corruption..