The tip that shows up states that you can't have waypoints further than 2000 meters apart. A common cause of this is the home point not being set properly.
If you home point is set properly then you might want to look at whether or not your waypoints are too far apart.
One thing to keep in mind is this also applies to the distances between the home point and the start and the home point and the end of the flight path. Those legs too must be less than 2000 m in length.