Where do we look to fix "Error in processing CC"

Shopping Cart is located: http://www.theoctagonfighter.com/catalog/default.php

When we get to the below screen and click on the continue button we get a red bar across the cart stating "There has been an error processing your credit card Please try again." and goes back to the payment information screen, seemingly asking a customer to re-enter the credit card number which people do and get charged twice because they are purchasing twice.

EPROCESSING SCREEN:--------------------------------------------------------

Secure Credit Card Transaction Processing
Thank you for your purchase. Your transaction has been successfully processed with the following response: APPROVED T32924



To complete your order, please click on the Continue button:
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***PAYMENT GATEWAY: EPROCESSING / USING THEIR MODULE / osCommerce 2.2-MS1
PLEASE SOMEONE HELP I'M GETTING ANGRY CUSTOMERS

osCommerce people say your gateway should be able to
trouble shoot it since I'm succeeding so far into the purchase.
My gateway Eprocessing tells me that I should talk to the
hosting company. Now Powweb is telling me to go back to
the osCommerce website where I have been at this for the last 2
days 14 hrs. a day

HELLLLLLPPPPPPP!!!!!!!!!!!!!!!!!!!!!!!!!!!

Please check your mailbox...

Paul