Object reference not set to an instance of an object

I'm currently getting a problem with using instantiate to fire a projectile, it works fine in the editor but not once built as webplayer or standalone.

The error I'm getting in the output log is:

**NullReferenceException: Object reference not set to an instance of an object at Elements.Update () [0x00000] in :0

(Filename: Line: -1)**

I have had a look at other examples with this happening but had no luck with implementing it into my code. Any help with sorting this out would be appreciated.

 #pragma strict
     
     static var element : int = 1;
     
     
     var bulletfire : Rigidbody;
     var bulletice : Rigidbody;
     var power : float = 1500;
     var damage : float = 100;
     var bulletcount : int = 10000;
     var gunshot: AudioClip;
     var allowfire : int = 1;
     
     
     function Start () {
       bulletcount = bulletcount;  
         
     
     }
     
       
     function checkgun () {  
       yield WaitForSeconds (0.5);
         allowfire = 1;
       }
     
     
     
     function Update () {
          
          
          
          
          if (Input.GetKeyDown ("1")){
                 element = 1;
         }
         
         if (Input.GetButton("Fire1")&& (allowfire == 1) && bulletcount && (element == 1)){
         
         allowfire = 0;
         audio.PlayOneShot(gunshot);
         var instance1: Rigidbody = Instantiate(bulletfire, transform.position, transform.rotation) as Rigidbody;
         var fwd1: Vector3 = transform.TransformDirection(Vector3.forward);
         instance1.AddForce(fwd1 * power); 
         bulletcount --;
         checkgun();
         }
         
     
         if (Input.GetKeyDown ("2")){
                 element = 2;
         }
         
     }