Not sure whats causing your problem, but have you tried dragging your music over in explore?
If not, right click on start and click on explore, find the music file you want to transfer and open it, it will open in the window on the right. Highlight the songs you want to transdfer and drag them to your external drive on the left, you can go to any file on the drive and drop your music.
This is the way I move my files around. Ron