These BY maps aren't made or sold by Garmin, they are cooperatively produced by KartaBy and afaik supplied without charge. "Roads of Belarus" (Dogori Belarusi) is made using Garmin's Map Product Creator (formerly Mapsource Product Creator). If the MPC software used to create the custom map is not licensed by Garmin then the resultant map will work fine in Garmin's older devices with unprotected firmware but will not work in newer devices with protected firmware. I don't know for sure if that's minay100's problem with his Camper 785 but it quite likely is the cause.