not able to go to shopping cart

-- url of the page with the problem -- : www.dekleinehelden.be
-- HikaShop version -- : essential
-- Joomla version -- : x.x
-- PHP version -- : x.x.x
-- Browser(s) name and version -- : XXXXX x.x.x
-- Error-message(debug-mod must be tuned on) -- : Error_message

Hi there,
For the first time a customer tried the paypal option on my website. It said 'this payment has not been completed and your account has not been charged'. So I tried to find out on your forum and support how to fix it. Could not find the solution. But testing a few options (like changing the 'address override') my shopping cart got stuck. It says it has two articles, but when I try to go there, I get a 'shopping cart is empty' message. I set everything back to the original settings and the problem with the shopping cart stayed. So now the first problem has not been solved and I have a new one.

Any ideas?
Thank you!
Sabine