OnTriggerEnter fails to activate

I have an object tagged as "Buster" flying through a trigger that should detect objects with the tag "Buster" and respond, but it does not. I have seen in other similar questions asked here the solution was found when they added a rigidbody to one of the objects. So I have added a rigidbody to the "Buster". Raycasts Hit Trigger is true. The trigger is a sphere collider with Is Trigger set to true.

This is the trigger script:

 #pragma strict
 
 public var HP : int;
 
 function Start () {
 
 }
 
 function Update () {
     
 }
 
 function OnTriggerEnter (other : Collider) {
     if(other.tag == "Buster"){
         HP = (HP -1);
     }
 }

This is the "Buster" script:

 #pragma strict
 
 private var left : boolean;
 public var time : float;
 public var speed : float;
 private var counter : float;
 public var xPosition : float;
 public var yPosition : float;
 
 function Start () {
 
     transform.position.x += xPosition;
     transform.position.y += yPosition;
     left = true;
     counter = 0;
 
 }
 
 function Update () {
 
     if (left) {
         if (time > counter){
             transform.position.x -= speed;
             counter++;
         }
         else {
             Destroy(this.gameObject);
         }
     }
 
     else {
         if (time > counter){
             transform.position.x += speed;
             counter++;
         }
         else {
             Destroy(this.gameObject);
         }
     }
     
 }