I did a quick search and didn't see anything. I just started to get Error 20's on my 5DII. I've had it about 3 years and it has about 10K clicks on it. It happens with various lens and cards. But when I pull the card out and shoot without it, it works, sort of. Any Ideas?
"Canon Error Codes Revealed
Direct from a source at Canon, we have the basics to shed at least a tiny bit of light on the various error codes Canon is using for the 5D Mark II and beyond. While none of these error codes reveal enough information to allow you to do repairs on your own, any amount of information can be comforting when dealing with these errors if they occur.
10 - Malfunction related to files has been detected.
20 - Malfunction related to the mechanical mechanism has been detected.
30 - Malfunction related to the shutter has been detected.
40 - Malfunction related to the power source has been detected.
50 - Malfunction related to the electric control has been detected.
60 - not used on 5Dm2
70 - Malfunction related to images has been detected.
80 - Malfunction related to the electric control of images has been detected.
90 - not used on 5DM2
These error codes relate specifically to the 5D Mark II but our source says they probably apply "across the board to all cameras after the 5D Mark2." So if you see any of these error messages in your camera, don't hesitate to send it in to Ted at Tallyn's for a warranty repair or repair quote. You can also join Canon Professional Service, which offers various levels of priority and attention to qualifying members."
George, in perhaps chasing down the "card culprit" you've mentioned, have you tried other cards besides the singular one you reference in you first post?
Have you also tried re-formatting any of the cards in a computer, instead of using the camera's built-in "OS"?