If you own a computer take it out of your Nikon reformat it in the your computer make sure before ejecting that it shows that you haven't used any memory on it basically it should say 0.0 gb used out of 59.5 gb because you will never truely get the whole 64 once formated if this doesn't work the card may be damaged if it's already showing red this also happen when any device is left on while your trying to insert it hope this was helpful. You haven't done anything wrong sometimes the SD card itself is defective.