Projectile not inflicting damage on AI

Hello. I have a projectile, but it is not casing damage. I tried using this line of code:

if(Physics.Rocket(Rocket, hit)){ // if something hit, send the message hit.collider.SendMessageUpwards("ApplyDamage", 800, SendMessageOptions.DontRequireReceiver);

and it would return Compiler errors. I don't know what to do. Also, my projectile script is below.

 // The reference to the explosion prefab
 var explosion : GameObject;
 var timeOut = 3.0;
 
 // Kill the rocket after a while automatically
 function Start () {
     Invoke("Kill", timeOut);
 }
 
 
 function OnCollisionEnter (collision : Collision) {
     // Instantiate explosion at the impact point and rotate the explosion
     // so that the y-axis faces along the surface normal
     var contact : ContactPoint = collision.contacts[0];
     var rotation = Quaternion.FromToRotation(Vector3.forward, contact.normal);
     Instantiate (explosion, contact.point, rotation);
     transform.Translate(Vector3.up * Time.deltaTime);
 
     // And kill our selves
     Kill ();    
 }
 
 function Kill () {
     // Stop emitting particles in any children
     var emitter : ParticleEmitter= GetComponentInChildren(ParticleEmitter);
     if (emitter)
         emitter.emit = false;
 
     // Detach children - We do this to detach the trail rendererer which should be set up to auto destruct
     transform.DetachChildren();
         
     // Destroy the projectile
     Destroy(gameObject);
 }