Sandbox Payment Error

[Bossler]

I am receving this error when testing a payment using my Paypal Sandbox Account for a clients website:

This transaction cannot be processed. The merchant's account is not able to process transactions.

There is no error number with the message, however I am assuming it might be either 10548 or 10549?

I am using the following test card generated from the Paypal Developer website:

Card Type: Visa Card Number: <removed>
Expiration Date: <removed>
CVV: <removed>

Can anyone point me in the right direction to troublsehoot this?

Thanks

Below is a snapshot of the error on the page that has the Paypal payment form. I am using Paypal Website Payments Pro in Sandbox mode with all my API info and gateway email address filled in.