What kind of music (mp3 or wav or ???) and what is the source?
Are you 100% sure the music files do not have DRM?
As John indicates, many music files (particularly from iTunes) have copy protection built into them that will prevent you from using them in a video project.
Along with the comments by both John T., and Steve G., there have been some issues reported with both of the two, Fixed Audio Tracks, Soundtrack and Narration. I do not think you have gotten that far yet, but wanted to point out the potential for those issues. Should you get your music Imported into the Project, but have issues when you use either Narration, or Soundtrack, just use an empty "regular" Audio Track.
Good luck, and please let us know more about your music files.