Step one is to format the card with the camera.

If the camera will not let you format the card you will need a card reader.

With a card reader, see if the computer can read the card. If it can.....delete all files and folders the computer can find on the card. Do not delete them to the recycle bin, hold down the Shift key before clicking delete. Then put the card back in the camera and format it with the camera.
Note: Do not format the card with the computer.

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