You will get the error message "The system can't execute the navigation program" if the iFly navigation app cannot be found. This can happen if the SD card is loose, missing, or if the wrong card is inserted, or if files have been deleted from the card, etc. The card can come lose if the iFly is dropped or bumped against something. You can contact support@adventurepilot.com and Ed will help diagnose the issue.
Thanks,
Walter