ok i just installed luma and i go on streetpass plaza and its saying my card is write protected and cant find the data i had on the card but i didnt press anything to make it write protected
i managed to fix it by turning streetpass of and on again in the game settingsIf you can tell us the name brand and storage capacity of microSD, it might help in determining if your issue is due to a fake card or your card is just defective, etc.
Otherwise you can only do data recovery with that card and put whatever files you can on a new microSD.