split credit card module rejects Mastercard

[Guest]

I have a split credit card option with cvv setup. We do this because we can process the cards offline when we ship because there can be inventory ordered which may be out of stock. Anyway, last night a customer tried to use a Mastercard and the cart advised her we don't accept Mastercard. The admin module asks you to check which of the 4 major credit cards (US) which you accept. Both Visa and Mastercard are checked yet the cart won't accept Mastercard, providing a notice which says something like "You entered a card which appears to be a Mastercard, but unfortunately, we don't accpt it at this time." Has anyone seen this problem before and how might it be fixed?

thanks,