If its happening on more then one card, then we know its the camera. Try doing this. Take the card clean off the gold plates with alcohol and cloth. DRY the card before puting it back in. after that put the card in. and pull it out half way, then put it back in. You can do this pretty fast cause. keep doing this 5-10 times. the idea of what we are doing is to try to clean off the connecters inside the camera because they can get build up. And if you using a card reader, or took it to a place to have you pictuers taken off the card it can put dirt in the camera. After doing that with the card take it out clean it off and try puting in the camera. Let me know if it works becasue i like to hear what happend
Thanks