It appears you may have cleared this up by now, as I can click your cart's PayPal checkout button and then select any country on PayPal's checkout site. If you still cannot, try clearing your browser cookies and then test it again.
For anyone else reading along here with a similar problem, your PayPal account has a setting to restrict your buyers' countries of residence, so that would affect the countries available to pick during checkout on PayPal's site.