Canon Mark III - access light on
while CF Card is so cheap nowadays, it is good to have one card for each camera.
because flipping back and forth sometimes does cause unnecessary hassle for both hardware and firmware of the camera, those dedicated gold plated connectors especially ... inside the card reader component. Back to the original situation, it can be folder corruption, just reformat the card in the camera you are using should solve 90% of the issues. Otherwise just get a card reader and format it in the computer.
When I place a CF Card, 4GB or 8GB from my 7D in my 5DIII, many a time, the access light stays on and never goes off doesn't matter how long I leave on. Is there anything wrong I am doing or is something wrong the camera is doing.
I understand you cannot pull out the CF or the battery while it is on.