i have same problem but this way i made it works


1. I pulled the battery out of the 770 to shut it down completely.
2. I inserted the battery back into the 770
3. I plugged the 770 back into its USB cable.
4. I turned on the 770 by holding down the home key (bottom-most button on the left) while simultaneously pressing the power button at the top. This put it into USB mode.
5. I started the updater and then allowed it to upload/update the new executable image for the 770.
6. The updater successfully finished updating the 770.