This issue had took me a month to solve.
It is very simple, my web site use US dollar as the currency.
And in the Currency Setup (System -> Configuration -> Currency Setup), “Allowed Currencies” multi-select box, I just picked only US dollar. That was my BIG mistake!
SOLUTION IS: select the country which is your origin shipping country.
Then I had an other problem: The UPS system return $0 or just your handling fee.
SOLUTION IS: configure your Currency Rates (System -> Manage Currency Rates)