Why can't I get music on my sidekick slide?

I've tried everything, I have a memory card, I tried syncing it with windows media and i tried drag and drop between folders... it loads the songs onto my music player but it wont play them i just get an error it says: Cannot Play Song danger.media.DRMNotSupportedException: System does not support DRM. What the heck is DRM and how can i get my songs onto my stupid phone???!!!! Help! Please!! Ahhhhh!!!