The programmer has investigated this for us and says the error is occurring as the card needs to be registered with Verified by Visa (now Visa Secure). This is an additional security measure to protect you from fraud when making online purchases and is separate from your bank or card issuer.
https://usa.visa.com/pay-with-visa/featured-technologies/verified-by-visa.html
Please register your card and then place your order again and let me know when you have done this so that I can check that it has processed correctly.
Please note:
Card MUST be registered with Visa Secure/Verified by Visa and your bank may require you to confirm the payment before it will process.
Finally when you enter your card details and hit "submit" please be patient and allow several minutes for the payment to process, we are aware that there is a "lag" but if you navigate away from the page, the payment will NOT process.