Despawner script returns null reference exception.

I'm currenly developing a 2D game in which you're to avoid some blocks which falls down. Do have them despawn after they leave the screen, I've created a cube that despawns anything that touches is, and that used to work perfectly.

That is until I added a scorepoint system. Basically, I want it to at 10 points to the score everytime a block despawns, as in everytime you dodge a cube, and that worked, but if you did hit a cube and died it just kept on counting. So I made a script which should check if you're alive or not, and stop the count of cubes if you're not, but I get a null reference exception when a cube hits my despawner. Heres my despawner script and my player movement script.

PlayerMovementScript

 using UnityEngine;
 using System.Collections;
 
 public class PlayerMovementScript : MonoBehaviour {
     public float Speed = 2.0f;
     public int Lives = 3;
     public GameObject Player;
     public bool CheckNumberOfShipsAlive = false;
         
     
     void FixedUpdate()
     {
         if (Input.GetKey(KeyCode.D))
         {
             transform.position += transform.forward * Speed * Time.deltaTime;
         }
         if (Input.GetKey(KeyCode.A))
         {
             transform.position -= transform.forward * Speed * Time.deltaTime;
         }
         if (Input.GetKey(KeyCode.R))
         {
             if (CheckNumberOfShipsAlive = true)
             {
                 Debug.Log("Respawn!");
                 GameObject spawnPlayer = (GameObject)Instantiate (Player);
                 CheckNumberOfShipsAlive = false;
             }
             else
             {
                 return;
             }
         }
     }
     void OnTriggerEnter()
     {
         Destroy(this.gameObject);
         Lives -= 1;
         CheckNumberOfShipsAlive = true;
     }
 }

DespawnerScript

 using UnityEngine;
 using System.Collections;
 
 public class DespawnerScript : MonoBehaviour {
     public float Score = 0.0f;
 
     void OnTriggerEnter(Collider other)
     {
         GameObject score = GameObject.Find("Player");
         PlayerMovementScript playerMovementScript;
         playerMovementScript = GetComponent<PlayerMovementScript>();
         if (playerMovementScript.CheckNumberOfShipsAlive = false)
         {
             Destroy(other.gameObject);
             Score += 10.0f;
             Debug.Log("Your score is " + Score);
         }
         else
         {
             return;
         }
     }
 }