It's actually not based on your credit card number or any sort of "credit card fraud" system, there's just a hard limit on the number of payments or registrations coming from the same IP in a short period.

If you have a friend or any other computer that has a different IP address (dial up connection?), you should be able to register using the same credit card number (or other payment method) without any issues.

Otherwise, you can call support or wait it out!