Sorry I couldn't help, but since it's working for me I'm still leaning toward a settings issue and not a software issue. iFly once held up a new release because I was having problems filing IFR flight plans with the beta version - there was no error, but they were consistently being filed as "no transponder" and ATC had to alter them when they were opened. After many emails and getting Leidos involved (who said they were being filed correctly), it turns out there was a new field in the ICAO aircraft setup that wasn't filled out, causing the problem. You might try filing to another US airport to see if it's only an issue with leaving the country, or an issue with all VFR flight plans.
Also, these forums are generally for iFly users to help iFly users, and sometimes we're no help. The best way to get support directly from iFly is to email support@adventurepilot.com. That email will get someone's immediate attention at iFly.
Good luck, and enjoy your trip!