Canon EOS-1D X Firmware 1.2.1 Firmware Version 1.2.1 incorporates the following improvements and fixes: The function to disable the Image size selection button has been added. Fixes a phenomenon in which Err 70 and Err 80 may occur during certain shooting conditions.

http://www.canonrumors.com/2013/01/canon-eos-1d-x-firmware-1-2-1-available/