The most common reason a credit card is not accepted is because the name and address specified for the web site account does not match the credit card information. All credit card companies require the name and address submitted for the purchase to match the information they have on file.
If this is the case, here is what you can do. Even though your license may be setup with a different entity, your account allows you create other names and addresses. After you login, click on the "My account" link at the bottom right. Then click on the "Address Book" tab. Then click on the link to add a new address. Make sure the name and address you use exactly matches the credit card.
Now when you go through the purchase process you can choose this name and address to use for payment (the license will still be associated with the original name and address).
If you still have problems, please call 615-371-1320 (9 a.m.- 5 p.m. US Central Time) to complete your credit card purchase over the phone.