During the process of updating with most recent firmware 1.1.3, the 5D Mark III I was using encountered a strange problem:
The firmware update would fail after reaching a certain amount of percentage of completion (avg. 52%), and would disable the camera from any other functions. I would not be able to use any function except for the automatic firmware update screen that would be displayed. I tried mounting a lens, pressed all buttons, but nothing would work. There wasn't a solution on the Canon website.
Even with several fully-charged batteries, several formatted CF/SD cards, the firmware update would still encounter an error. I even tried re-updating to the 1.1.2 version, but it still wouldn't work.
After almost an hour I finally found a solution:
From of an "ah, why in the world not?" idea, just for the sake of doing it, I used the BG-E11 with two batteries, and the update went all the way to 100% and completed.
Now, I have no idea why this would happen, but has this phenomenon happened to any other 5D Mark III bodies out there?