Rhapsody music transferred from Clip plays on one computer but not another

This is my first mp3 player and I’m a total newbie.  I got the Rhapsody To Go trial with my new Clip.  I’ve authorized two computers to use the account.  Some tracks I’ve transferred play on both machines (no DRM?).  Some of them won’t play on the first machine authorized, and request DRM rights, but they play with no problem on the second machine authorized.  Any ideas on why this is, and how I can get them to play on the first machine? Thanks.