It's the Windows version. But the song is from a previous version. I think I've narrowed it down now...it's an instrument that I added to a Style, a Steel Guitar. It's just not regenerating. When I try to regenerate a section of it with Track Actions, there is a message saying "There is no RealTracks on this Track. Would you like to select one?". I freely admit I'm not a whiz in BIAB, but this is weird to me. I think I can hack a workaround, but I'm just not sure why it's happening.