Goggs wrote in post #18568831
Hi Yes I have used different cards and the same thing.
I really meant have you bought a new card and tried it, just to rule out an OS thing on the old cards and old reader. Have you tried to format the cards, and also have you tried a different card reader, or different computer? The idea here is to completely rule out cards and the computer and the reader as culprits to point squarely to the 5D3 as the issue.
Also for clarification...
When you take a picture, and it writes it to the card (SD or CF?), are you able to move between all the pictures on the camera and view them? It is only after you take the card out and put it into a reader that when it goes back, there are no files? If that is the case, this certainly doesn't seem like a camera issue.
You can rule out the camera as the issue too by plugging a USB cable from the computer to the camera and view the images that way without messing with the card. If the computer doesn't see the files, that would lead to a Canon problem.