Problem with Instantiated clones

Hi, I have a spawner with the following code: using UnityEngine; using System.Collections;

 public class Spawn : MonoBehaviour {
 
     public GameObject[] enemies;
     public int amount; 
     private Vector3 spawnPoint; 
 
 
     void Start() {
         amount = 2;
 
     }
 
     void Update () {
         enemies = GameObject.FindGameObjectsWithTag ("Enemy");
         amount = enemies.Length;
 
         if (amount < 100) {
             InvokeRepeating ("spawnEnemy",1,100f);
         }
     }
 
     void spawnEnemy() {
         spawnPoint.x = Random.Range (-20,20);
         spawnPoint.y = 0.5f;
         spawnPoint.z = Random.Range (-20,20);
 
 
 
         Instantiate (enemies[Random.Range(0, enemies.Length -1)], spawnPoint, Quaternion.identity);
     
         CancelInvoke();
     }
 
 
 
 }

I also have the code to make the enemies move, which looks like this:

 using UnityEngine;
 using System.Collections;
 using UnityEngine.UI;
 
 public class EnemyMove : MonoBehaviour {
 
     public Transform track;
     private float moveSpeed = 3;
 
     public int score;
     public Text scoreText; 
     public int health;
     public Color damageColor = Color.red;
     Renderer rend;
 
 
 
 
 
     void Start() {
         PlayerPrefs.GetInt ("scorePref");
         score = PlayerPrefs.GetInt ("scorePref");
         health = 1000; 
         rend = GetComponent<Renderer> ();
         rend.material.color = Color.white;
     
 
     }
 
 
     void Update () {
         float move = moveSpeed * Time.deltaTime;
         transform.position = Vector3.MoveTowards (transform.position, track.position, move);
 
         PlayerPrefs.SetInt ("scorePref", score);
         if (scoreText.name == "Score") {
             scoreText.text = "Score: " + score;
         }
 
     
     
     }
     void OnTriggerEnter(Collider col) {
 
         if (col.gameObject.tag == "Bullet") {
             PlayerPrefs.SetInt ("scorePref", score);
 
             rend.material.color = damageColor;
 
             health -= 100;
             print ("I've lost health!");
 
             if (health <= 0) {
 
 
                 Destroy (GetComponent<MeshRenderer> ());
                 Destroy (GetComponent<BoxCollider> ());
                 Destroy (gameObject, 5);
 
             }
 
         
 
 
         
         
 
         }
         if (col.gameObject.tag == "Player") {
             Destroy (gameObject);
             Debug.Log ("Outch");
 
 
         }
     
 
 
 
     }
 
 
 
 }

When the object "Bullet" collides with the Enemy, the material changes to red. However, I sometimes get an error which says that some of my clones don't have a Renderer attached to them, even though the prefab "Enemy" which is being spawned does have a Renderer.

As well as this, does anyone know how to use PlayerPrefs to add to the score in the code?