The card may have a corruption or a file has been damaged. Many card corruptions are often a result of human error, awareness on the how the corruptions may occur can help prevent them.
| Turning the camera off mid transfer - while the image is being transferred to the card | 
| Power failure – battery low | 
| Opening the card door while an the image is being transferred | 
| Rapid shooting – some cameras need more time to transfer images | 
| Viruses up-loaded to your camera via the usb port | 
Refer to link: Card recoveries
Important:
Re-format the card, don’t delete all. Recommended to re-format in the same camera
We recommend using several smaller cards instead on one large card. If a problem does occur you have a card as a back up and the more images stored on your card the longer it takes to transfer.
Use good high standard cards.