Hi,
I'm in test mode for authorize.net AIM, and I'm able to test visa and mc, but when I tried discover or amex, it says that . I'm using the test cc numbers that the admin>modules>payment> telling me to use. The message that comes up when I tried discover:

The credit card number starting with 6011 was not entered correctly, or we do not accept that kind of card. Please try again or use another credit card

Is there a setting somewhere to test the other 2 card formats?