How to solved this for my soldier at Assets/AIScripts/WanderBehavior.cs:71)
void LateUpdate() { transform.position = new Vector3(transform.position.x, Terrain.activeTerrain.SampleHeight(transform.position), transform.position.z); } }
Edit
Try dropping Terrain :
activeTerrain.SampleHeight is enough.
Your confusion arises from a misunderstanding of the docs : activeTerrain is a static member of the class Terrain, used to access easily the active terrain.