Quaternion To Matrix conversion failed because input Quaternion is invalid

I suddenly got this error. I don't know what went wrong. I can still play my game, but I get this error when I slide my character.

 using UnityEngine;
 using System.Collections;
 
 public class CameraController : MonoBehaviour {
 
     private GameObject player;
     PlayerController playerController;
 
     public float cameraHeight = 4;
     public float cameraDistance = 4;
     public float smooth = 3;
 
     private float newCameraHeight;
 
     private int direction;
 
     // Use this for initialization
     void Start ()
     {
         player = GameObject.Find ("Player");
         playerController = player.GetComponent<PlayerController>();
 
         transform.position = new Vector3 (player.transform.position.x, cameraHeight, player.transform.position.z);
         newCameraHeight = cameraHeight;
     }
     
     // Update is called once per frame
     void Update ()
     {
         float speed = playerController.runSpeed;
         direction = playerController.getDirection ();
 
         if(newCameraHeight < cameraHeight)
         {
             cameraHeight -= 0.1f;
         }
         else if(newCameraHeight > cameraHeight)
         {
             cameraHeight += 0.1f;
         }
 
         Vector3 MoveTo = new Vector3 (player.transform.position.x, cameraHeight, player.transform.position.z);
 
         switch(direction){
         case 0:
             MoveTo += new Vector3(0, 0, -cameraDistance);
             break;
         case 1:
             MoveTo += new Vector3(-cameraDistance , 0, 0);
             break;
         case 2:
             MoveTo += new Vector3(0, 0, cameraDistance);
             break;
         case 3:
             MoveTo += new Vector3(cameraDistance , 0, 0);
             break;
         }
 
         transform.position = Vector3.MoveTowards (transform.position, MoveTo, speed);
 
         Vector3 LookAtVector = new Vector3 (player.transform.position.x, player.transform.position.y + 2, player.transform.position.z);
 
         // Create a rotation based on the relative position of the player being the forward vector.
         Quaternion neededRotation = Quaternion.LookRotation(LookAtVector - transform.position);
         
         // Lerp the camera's rotation between it's current rotation and the rotation that looks at the player.
         transform.rotation = Quaternion.Lerp(transform.rotation, neededRotation, smooth * Time.deltaTime);
     }
 
     public void changeHeight(float height)
     {
         newCameraHeight = height;
     }
 }