Trying to erase an sd-card

I have a 2gb sd-card that was in my 3ds but i was going to transfer it to my wii U. I plugged the sd-card into my macbook pro running mac OS X 10.10.4 and i cannot erase the card. I opened disk utility and the format option is grayed out. The sd-card is formatted with ms-dos FAT and is unlocked. i have tried putting the switch on the card halfway between locked and unlocked and that did not work any suggestions?