On the canon 7D there is a screw on the bottom board that comes loose and moves around in the camera and eventually sticks to something. When I see this error code this is usually the case for me and an easy fix. You will have to take off the back cover and there is a flex for the card reader that is connected to the main board on the lower right of the board. You would have to remove the flex from the board and use a light source to look at the bottom board to see if the screw is missing. I usually find the screw by tape around the view finder area when the back cover is off. I also find it when taking the front cover off and it will be stuck to the shutter motor. Usually after finding that screw it cures the error and the camera will work as should. To take off the back cover there is four screws on the back around the viewfinder, three on the bottom and one under the grip on the back cover. Be careful when removing the back cover as there is a flex connecting the back cover to the main board.