Ed has a 13" MacBook Pro and after moving his music over using iTunes, he now has duplicate files and they won't play anything. Leo says what you want to do is import the music and not make a copy of it. That will tell iTunes where to go to access the music. So now, Ed will need to get a dedupe app to remove the duplications. Or you can search for everything that includes "copy 1" and "copy 2" and delete them. Then reimport them without "making a copy" enabled. That will reindex iTunes, pointing to where the files live on your external drive.