I've got the same issues as 'yourdigitaldave' using the Canada Post plugin - but we're just shipping in Canada only. We get the same error message:
Sorry, it seems that there are no available shipping methods for your location (Canada). If you require assistance or wish to make alternate arrangements please contact us.
I've made sure that the sizing and weights are the same throughout the website for consistency, the store's base country is set for Canada as are the dollars (CDN), the Canada Post API settings were double-checked, and the same error message comes up in Safari, Chrome, and Firefox. Also, as of today, I updated the WooCommerce to it's latest version 2.0.7.
I created a WooCommerce ticket a few days ago (http://support.woothemes.com/requests/38994) but no response so far.
If someone out there has a solution, please share!!
Many thanks!