On the listing just ended your shipping costs don't seem to be working for Canada or any other country. Which shipping option were you using for Canada, the U.S. and for other countries?
If you were using expedited USA more than likely the problem was the measurements as the minimum measurements for that service are bigger than for most other services.
If you entered less than 21cm x 14cm x .5cm, the calculator wouldn't work. But that doesn't explain why shipping wasn't work for other countries.