If you EFILE a return that includes form T1273 Statement A: Harmonized AgriStability and AgriInvest Programs Information and Statement of Farming Activities for Individuals, and that you entered information for the Contact Person but omitted to select the checkbox Do you want a copy of your Calculation of Program Benefits (COB) for the AgriStability program sent to your contact person?, you will most likely end up with an invalid XML file.
Workaround
You must select the checkbox Do you want a copy of your Calculation of Program Benefits (COB) for the AgriStability program sent to your contact person? prior to EFILEing the return.