There's a route I do about twice a year for an overnight camp, following a route on the 530, and every time on the outward journey that I get to a particular stretch of road, the Garmin starts bleeping at me and telling me to make a U turn - even thought there were no wrong turns available for me to take before the "error message" and even though I know I'm on the right road in the right direction and the map view on the Garmin shows the route and that I'm on it in the right direction.
I did consider that there might be an issue with the .gpx file that I uploaded and I have tried deleting it and recreating it - albeit using the same online planner - I still get the error on that stretch of road.