Placing objects error

 #pragma strict
 var cb : GameObject;
 
 function Update () {
     if(Input.GetButtonDown ("Fire1"))
     {
         var instance : GameObject = Instantiate(cb, transform.position, transform. rotation);
     }
 }

This is my script called plc for placing copies of object cb...

 #pragma strict
 
 function OnCollisionEnter (collision : Collision){
     collision.transform.GetComponent(plc).enabled = false;
 }

This is script what disable plc script when happen collision between object and copy of that object. (Simply I don´t want to have to two or more objects in row). This scripts are for "creator mode" in game... Can somebody help me? I´m lost...