I have been using my D600 for two years without any problems until this weekend. I had two 64 GB cards in the camera one PNY and the other Delkin. After taking about 150 pictures I got an error message "card error" and the camera would not take another picture. I remover the first memory and after 15 more shots I got the same message again. I turned the camera off and inserted both memories and took a few more pictures without getting the message. When I downloaded the files the last batch of images were missing! Right now the camera seems to be operating normally. I was taking pictures out doors the temp was about 40 deg. F. What happened?