I do not get a shopping cart empty message when I test your site, i get this message instead:
Unable to process payment. Please contact the merchant as the shipping address provided by the merchant is invalid, and the merchant has requested that your order must be shipped to that address.
on the confirm page, change:
<input type="hidden" name="address_override" id="address_override" value="1" />
to:
<input type="hidden" name="address_override" id="address_override" value="0" />