Incidentally, I had this problem too, I think. It was copying fine until I got to 89%, but when I popped the 4th disc in it slowed to a crawl and then stalled out completely about half a GB into the 4th disc. Tried it again, exact same thing.
I started over in offline mode and it worked. After it was done, I put Origin back online and it automatically started downloading the DLCs. Thanks to JoxerTM22 for the solution; that wouldn't have occurred to me!
