You may find the copy process is more reliable by installing sshd and running the commands remotely. I had osso xterm crash on me during the copy. Also best to only try the copy step after a clean boot with nothing running.

(Funnily enough after this ran successfully I got a white screen of death and have only just got my 770 replaced and back up and running. Fortunately this was the last thing I did so at least I had a perfect copy of my system on the mmc card :-))

Cheers,
-John