If you get errors like that, it doesn't have anything to do with the software installation: it's all a network problem OR it's a problem between Esellerate and your bank or credit card company. We don't have any control over that, we don't have your credit card details and we don't get any report of any error that might have happened during the connection between your machine and the Esellerate servers, or any error that might have been returned for any reason related to credit card authorization. It's all handled via Esellerate.
You can either try to contact them to support@esellerate.net OR you can try buying on the web ( using the "Buy on Web / PayPal" button ), because that procedure works either with PayPal or Credit Card, and is using the browser instead.