all save files corrupted? m3ds real

So i downloaded the last update for my m3dsreal and all my save files stopped working! Sure I have way ay more cheats now but I had games with like 300 gameplay hours.
Is there any way that I can fix this? cause I really want my save files back but I don't want to delete the update!
( Had like 12 games with animal crossing(no cheats) all golden tools and stuff, thats why I really want my save files back)

Backup your save files (and game files too), format your card and revert to the older firmware to see if they are really corrupt or if something went wrong with the firmware update.If they work again, then try to update to the correct latest firmware and see if it happens again.

If not, perhaps something changed with the save creating.