Cast Source Instantiating Error

Unfortunately I have run around again now with an odd casting source error that I cannot seem to resolve. Basically I have a rocket (instantiated) that should explode (instantiate an explosion) upon contact with its collider.

Right now the collider IS set as a trigger, and the explosion is a prefab. This is the exact error that I am getting:

InvalidCastException: Cannot cast from source type to destination type.
RocketBlowup.OnTriggerEnter (UnityEngine.Collider other)   (at Assets/MainFolder/Scripts/RocketBlowup.js:5)

The code I am using is a simple "On trigger enter" function which is attached to the rocket. The error seems to be pointing directly to the instantiation line of my code - which is completely correct I believe:

var explosion : Transform;
var blowuppoint : Transform;
function OnTriggerEnter (other: Collider) {
    var expl : Rigidbody;
        expl = Instantiate(explosion, blowuppoint.position, blowuppoint.rotation);
       Destroy(gameObject);
}

The "blowuppoint" is simply an empty gameobject positioned behind the rocket so that the point of explosion is in the right place.

Thanks in advance, CarbonTech Software Admin