I am using the authorizenet_aim module to accept credit cards. I have successfully received orders with mastercard and visa. I just got an email from Discover saying that we have something set up wrong. So I put the shop back into test mode and authorize.net into test mode and endered the test Discovercard #. It doesn't accept it. I tried turning off and on Discover card in configuration>credit cards...

When Discover card is off and I run a test I get a red box that says " The first four digits of the number entered are: 6011. If that number is correct, we do not accept that type of credit card. If it is wrong, please try again."

When Discover card is on and I run a test and get "(TESTMODE) The merchant does not accept this type of credit card. - Your credit card could not be authorized for this reason. Please correct any information and try again or contact us for further assistance."

What should I try next?

-Chris