Paypal throws a page not found

I installed the shopping cart and all worked fine until recently. When visitors use the ‘add to cart’ option, Paypal now throws an error: “Page not found”.

The plugin seems to link/try to open the link https://www.paypal.com/cgi-bin/webscr but ends up at https://www.paypal.com/webapps/mpp/page-not-found