Now you have a 5D Mark III and you decide to use your old lens adapter. You don’t think twice as this combination of (insert mount) to EOS has worked solid for you in the past.
Come to find out if there is a chip in your adapter (refer to bottom image), the Canon 5D Mrk III will generate Err 01 “Communications between the camera and lens is faulty. Clean the lens contacts.” After wiping the sensor of my Fotodiox lens adapter, I realized this issue was deeper. The Mark III does not work with chipped adapters, at least not ones that worked on your Mark II. Buy yourself a cheap non chipped adapter, the route I wish I had gone back in the day since the focus assist functionality was never of much use to me.
luckily I had just got the camera body from Federioco at Los Angeles Camera Rentals who is more than willing to help his customers. He met me at his office, on a Saturday, as surprised as I was about my lens mount discovery. He quickly gave me some Canon lens’ free of charge knowing I was budgeting to use my Nikons. I highly recommend Los Angeles Camera Rentals for when the budget matters and you need the basic essentials to get your shoot underway. This is the only shop I could find in LA that rents the Panasonic GH2 with Voigtlander lens’. He also rents the FS100, Red Scarlet, lights like Kino Flos, and Litepanel amongst other equipment.