I can't keep downloading this file. What do I need to do? I can't keep downloading this file. What do I need to do?
It looks like GarageBand cannot write to the User Library to remember that it already downloaded the additional contents.
I'd try HangTime's fix for oddball probs, i.e. delete GB's preferences and repairing permissions on your computer, as described in the FAQ:
After that you may have to reindex your loops, since GarageBand did not successfully finish the installation of the loops, see: Rebuilding the Loop Index in GarageBand