We use PayPal Website Payments Pro to process our credit card form, and they may be blocking your transaction as part of a fraud prevention strategy. It may also be that you are trying to make a purchase from a country PayPal does not support.
You could try checking out using the PayPal option we provide. This process is separate from PayPal Website Payments Pro, and sometimes payments work using PayPal directly, even if they don't work when you use our credit card form.
There is also a possibility that your financial institution blocked the payment in order to protect you from potential fraud. In that case, the best thing to do would be to contact your financial institution and confirm that your purchases from us are legitimate purchases by you.