Hi,
I am having the same problem, plus a couple of additional ones that I think are all linked into the same problem. I have tried both the email address I use for PayPal, and the secure PayPal number, both with the same result. The additional problems I am having are that I can add one item to the cart, but when I add a second item from the same page, it replaces the first item. If I go to a different page to add an item, the first item is gone and the cart is empty as soon as I arrive at the page. Just a further piece of information that may or may not help, I had originally tried a few “add to cart” buttons from PayPal, and they worked fine, but I have since deleted them, and am going with the eStore buttons because PayPal France does not have the option of weight-based shipping options.