All right, so you either accidentally or purposely (boneheaded move!) went ahead and updated your DSi or 3DS to the newest 1.4.2 firmware and you got the dreaded card not recognized error! Well, your worries are over. No, you cannot roll back the DS firmware to a compatible firmware version (unless you know something the rest of the video gaming world does not) but you can update many of the newest DSi and 3DS carts to work flawlessly on this firmware.
The following Backup Units have been updated and have downloadable updates to support the 1.4.2 firmware:
So we’ve got you covered for this update, but in the future, do not update your firmware! Unless of course you don’t mind losing the functionality of your precious flash cart. And if you’ve got one of those old clunker cards (oh the shame!) now is the perfect time to get one of the newest and best cards.