Canon EOS-1D Mark III Firmware Version 1.3.1
Canon has issued a firmware update for its EOS-1D Mark III digital SLR camera. Version 1.3.1 enables focusing with the central AF sensor when the camera is used with the EF 200-400mm F4L USM Extender 1.4X lens and an Extender whose combined maximum aperture is f/8. You can download the firmware upgrade from the website below.
Website: Canon EOS-1D Mark III Support