It can happen on a number of reasons. We recommend the following solutions:
1) Check out if your card is available for international payments;
2) Check out if your card limit is not exceeded;
3) Try to use another browser;
4) It seems, your bank has taken safety measures due to anti-fraud policy when you tried to buy. Call to your bank to validate the payment.
5) Try to change the method on PayPal (a line "Payment method", below the address). Even if you don't have a PayPal account, you can use this method. Click "PayPal checkout" => "Create an account" => put your card data.
6) Get in touch with us for alternative methods of payment.