No - I have my RealTracks on Drive F (drive C being too small), my colleague has a large enough hard drive to keep everything on Drive C. If the BIAB files we're exchanging depend on explicit paths to the RealTracks, this could well be the problem.

It doesn't explain how Play=>Generate (...) fixes things on the destination machine, though, nor does it explain why my exported-to-iPad songs lack RealTracks unless I force re-generation from the iPad.