If you are formatting the card for use in a device (cam, phone etc.) I suggest you format it directly on the device it will be used on. It may sound stupid, but you will get the best results that way!
some times the card gets corrupted or wear leveling takes its toll so only a low level format will work sometimes, try this software from panasonic I've had luck with it on a few cards: http://panasonic.jp/support/global/cs/sd/download/index.html