Script error HELP

So i keep getting a weird error that i don’t have it set or something Error is:NullReferenceException: Object reference not set to an instance of an object
Boo.Lang.Runtime.RuntimeServices.InvokeBinaryOperator (System.String operatorName, System.Object lhs, System.Object rhs)
Water Physics.Update () (at Assets/Scripts/Water Physics.js:13)
I have no idea what it means my code:

//deathnadosharkgames
var waterLevel : float;
var floatHeight : float;
var bouncedamp : float;
var offtheset : Vector3;

private var forcefactor : float;
private var actionpoint : Vector3;
private var uplift : Vector3;

function Update () {

	actionpoint = transform.postion + transform.TransformDirection(offtheset);
	forcefactor = 1f - ((actionpoint.y - waterLevel) / floatHeight);
	if(forcefactor > 0f) {
	
	
	uplift = -Physics.gravity *(forcefactor - rigidbody.velocity.y * bouncedamp);
	rigidbody.AddForceAtPosition(uplift, actionpoint);
	
	
	}
	

}

Null reference exception is when something in your script is referring to a thing which doesn’t exist.

line 13:actionpoint = transform.postion + transform.TransformDirection(offtheset);
note, transform.postion
that is probably what it’s complaining about.