authorize.net sandbox testing errors "The merchant does not accept this type of credit card"

I am using the testing guide (http://ift.tt/1GZwRZ6) to test on the authorize.net sandbox environment. The visa and mastercard and jcb card numbers were successful, but american express, discover, and diners club cards failed: "Transaction Error : 17 The merchant does not accept this type of credit card."

Why would the test environment not accept those cards, or it something else? Please advise.

Thanks

(my code used the sample code from: http://ift.tt/1Gw4pTK)