Help with music transfer to external HD

So I have an imac and a G_drive external and I am trying to backup all of my itunes library as well as all of my garage band files. When I begin the transfer a message keeps popping up saying certain items are "in use" which makes no sense to me because itunes and garageband are both not in use and are closed. what the **** is going on?
thanks.

repair permissions, and restart. then try again.

just tried this and still having the same problem. thanks for the help, any other suggestions?

what specifically are you dragging over? particularly the garageband stuff.

dragging the "itunes music" folder located under the music tab on my HD. for the garage band i am dragging the "Garageband" folder under the music tab.
Thanks

so are you trying to "move" or "copy"? have you tried copying and pasting, not dragging?