PayPal error while trying to pay with credit card in sandbox

Question

While testing the direct payment with credit card I always get the following error: "You cannot use an e-mail address or card number that belongs to an existing PayPal account. If you have a PayPal account, please log in. If you don't, please change the e-mail address or card number and try again". The credit cards number I use for testing come from http://www.paypalobjects.com/en_US/vhelp/paypalmanager_help/credit_card_numbers.htm but I also tried those produced by http://www.getcreditcardnumbers.com/ .

Answer 1

Finally I found the solution by cleaning browser cache and cookies before to connect to my site. It's strange but it seems that having a PayPal cookie in the browser (created by during a previous PayPal transaction) causes its use also during a guest payment attempt.