Vickie,
To cut to the chase: A couple of problems here...."Priority International" is specified twice and it overlaps between Worldwide and Canada. On the entry for second service, you need to *check all but Canada* instead of checking worldwide to avoid the error. Due to the overlap, the shipping calculator would not know how to handle Canada...that's why eBay kicked it back with an API error.
Also FYI...USPS Priority Mail int FLAT RATE BOX to Canada and USPS Priority Mail Int on all the other countries are actually the *same service*, so doing that won't fix the issue.
The key is to check one to Canada and then check all but Canada rather than Worldwide.
Hope this helps.