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?

hmmm… Maybe the bullets are colliding with other gameobjects without renderer.
For example, terrain…

try to add this…

if(rend != null) //do something

or

if(this.GetComponent() != null)// do something.