Track target

Ok that was easier than I thought it would be, but I have another problem, if I drop a game object onto target in the inspector it tracks it as expected, but if I drop a prefab onto target in the inspector when the prefab is initiated it does not track it, why?

The first script is the tracking script, the second is throw Grenade script, In the throw grenade script it turns on the Track Grenade game object so the tracking script will run, then just before destroying the Grenade game object turns it off again.

Thanks.

 #pragma strict
 
 var target : Transform;
 var trackIcon : Texture2D;
 
 function Awake(){
 
 }
 
 function Start(){
 
 }
 
 function Update () {

     var screenPos : Vector3 = Camera.main.WorldToScreenPoint (target.position);
 }
 
 function OnGUI(){
 
     var screenPos : Vector3 = Camera.main.WorldToScreenPoint (target.position);
     var reverse : float = Screen.height;
     var clampX = Mathf.Clamp(screenPos.x, 0, Screen.width - (trackIcon.width / 2));
     var clampY = Mathf.Clamp(reverse - screenPos.y, 0, Screen.height - (trackIcon.height / 2));
     
     GUI.DrawTexture(Rect(clampX, clampY, trackIcon.width / 2, trackIcon.height / 2), trackIcon);
 }

 #pragma strict
 
 var grenadeExplosion : Transform;
 var Explosion : Transform;
 var explosionSound : AudioClip;
 var hitSound : AudioClip;
 var trackGrenade : GameObject;    // Referance to the GameObject with the TrackTarget on
 
 private var creationTime : float;
 private var loop : boolean = true;
 private var boxCollider : BoxCollider;
 private var playerDamage : GameObject;
 
 function Awake(){
 
     creationTime = Time.time;
 }
 
 function Start(){
 
     trackGrenade = GameObject.Find("Track Grenade");
     playerDamage = GameObject.Find("Main Camera");
     trackGrenade.gameObject.SetActive(true);
     boxCollider = transform.GetComponent(BoxCollider) as BoxCollider;
 }
 
 function Update(){
 
     if(Time.time > (creationTime + 4)){
         destroyGrenade();
     }
 }
 
 // Apply damage to the Player acording to where they are in the blast range
 function AreaDamageEnemies(location : Vector3, radius : float , damage : float ){
 
     var objectsInRange : Collider[] = Physics.OverlapSphere(location, radius);
     
     for (var col : Collider in objectsInRange){
         var player : FirstPersonControl = col.GetComponent(FirstPersonControl);
         if (player != null)
         {
 // linear falloff of effect
             var proximity : float = (location - player.transform.position).magnitude;
             var effect : float = 1 - (proximity / radius);
             
 // Apply damage to the Player in the PlayerDamage.js on the Main Camera game object (Player)
             playerDamage.GetComponent(PlayerDamage).ApplyDamage(damage * effect);
         }
     }
 }
 
 function OnCollisionEnter(collision : Collision) {
 
     audio.volume = 1.0;
     audio.PlayOneShot(hitSound);
     }
 
 function destroyGrenade(){
     
 if(loop == true){
     loop = false;                                    // Set loop to false so this destroy() function dont keep repeating
     AreaDamageEnemies(transform.position, 10, 10);    // Set the blast radius of the Grenade and call AreaDamageEnemies function above
     boxCollider.size = Vector3(0,0,0);                // Resize the Box Collider down to 0 so you dont get an error with the
                                                     // RayCast trying to access it after the Grenade has been destroyed
     Instantiate(grenadeExplosion, transform.position + Vector3(0, 0, 0), Quaternion.identity);
     renderer.enabled = false;                        // Turn off the mesh render so you dont see the Grenade while the explosion effect and explosion sound sample play out
     Instantiate(Explosion, transform.position + Vector3(0, 0.7, 0), transform.rotation);
     audio.volume = 2.0;
     audio.PlayOneShot(explosionSound);
     yield WaitForSeconds (3.0);
     trackGrenade.gameObject.SetActive(false);
     Destroy (gameObject);                             // Destroy the Grenade
     }
 }