If this only happens with RealTracks (esp. ones with lots of RealTracks), it could be that your computer's CPU is too slow to keep up with generation of the song as the song plays. If this is the case, try disabling PRefs-RealTracks-Speed Up Song Generation. Disabling this will make a delay prior to the song starting, while the entire song generates, but it will insure that the whole song is generated. Next, check the speed of your PC, by running a geekbench (google that to download it).. You need about 1,500 geekbench to generate songs in the backkground like that.

Have Fun!
Peter Gannon
PG Music Inc.