Without further information, I would guess that "Business" probably threw them off. When I did the interview, the agent had a printout that with all the allowable card types (Visa Platinum, Visa Signature, Mastercard World...etc) and matched my card word-by-word. I vaguely recall that he list did not contain anything with the word "Business" on it.

If you can't think of anything else that might have led to the denial, I would apply again with a personal credit card.