NullReferenceException: Object reference not set to an instance of an object

Hello everyone,

I just purchased Top-Down Dungeons [Mobile] and added all my game prefabs correctly. But when I try to walk (move) with my player, I get this fatal error:

NullReferenceException: Object reference not set to an instance of an object PlayerScript.CheckTerrain () (at Assets/Scripts/PlayerScript.js:162) PlayerScript.MovePlayer () (at Assets/Scripts/PlayerScript.js:200) PlayerScript.FixedUpdate () (at Assets/Scripts/PlayerScript.js:41)

Can anyone help me to fix this?

159-164 lines:

 function CheckTerrain() {
     var MoveTarget = GameObject.Find("MoveTarget").transform.position;
     var MyY = transform.position;
     if (Terrain.activeTerrain.SampleHeight(MoveTarget) -1 > Terrain.activeTerrain.SampleHeight(MyY)) return false;
     else return true;
 }

191-204 lines:

 if (Input.GetKey ("mouse 1")) {
             if (Input.mousePosition.x >= Screen.width - Screen.width/6) { if (!animation.IsPlaying("idle")) AnimationPlay("idle"); return; }
             playerPlane = new Plane(Vector3.up, transform.position);
                ray = GameObject.Find("Main Camera").camera.ScreenPointToRay (Input.mousePosition);
                hitdist = 0.0;
                if (playerPlane.Raycast (ray, hitdist)) {
                    targetPos = Vector3(ray.GetPoint(hitdist).x,0,ray.GetPoint(hitdist).z);
                 transform.rotation = Quaternion.LookRotation(targetPos - Vector3(transform.position.x,0,transform.position.z));
                 if (Vector3.Distance(targetPos,transform.position)<9) { animName = "walk"; speed = 5; } else { animName = "run"; speed = 12; }
                 if (MoveCanSee() == true && CheckTerrain() == true) transform.Translate(Vector3.forward * Time.deltaTime * speed);
                 if (IsMultiplayer == 1) UpdateTransform();
             }
     if (!animation.IsPlaying(animName)  && !animation.IsPlaying("spellcast")) AnimationPlay(animName);
 }

and 39-42 lines: function FixedUpdate () { if (IsMultiplayer == 1 && nextCheckMP < Time.time) { nextCheckMP = Time.time + 1; CheckMP(); } if (Died == 0) MovePlayer(); }