Try putting it in a bag...
The ATM in my store can be a bit tricky. We've discovered (somehow) that when it won't read a card, there's an 80% chance of it reading that card if the card is in a plastic bag when swiped. (as in, put card in bag, swipe bag through the card reader, with the card's stripe lined up in the right spot, etc.)
Customer: "The ATM's not reading my card."
Me: "Sometimes it will work if you put your card in a bag." *hands customer a plastic bag*
Customer puts the card in the bag, takes it out again, and swipes the card.
the weird thing is, it worked.