(Last change and then we're good to merge.)

PathDesiredHandle() will equal NULL only if this UAVO hasn't been instantiated. That occurs when the path follower is not running. So you could say "The PathFollower module is not running. This module must first be enabled in the Modules tab."

On a side note, SYSTEMALARMS_MANUALCONTROL_PATHFOLLOWER is not used in the error code handler so that needs to be fixed in another PR.