object is not a member of 'UnityEngine.Component'.

From what I can tell nothing is wrong…

Assets/Scripts/Pickup.js(7,96): BCE0019: ‘hand’ is not a member of ‘UnityEngine.Component’.

#pragma strict

function OnTriggerEnter (other : Collider){
	if(other.gameObject.tag == ("Player")){
		other.gameObject.SendMessage ("ItemPickup", transform.parent.gameObject);
		transform.parent.gameObject.rigidbody.isKinematic = true;
		transform.parent.gameObject.transform.parent = other.GetComponent("Inventory").hand.transform;
		transform.parent.gameObject.transform.position = other.GetComponent("Inventory").hand.transform.position;
		transform.parent.gameObject.transform.active = false;

GetComponent is returning… a component. Unity components don’t have hands.

You want an Inventory, and the easiest way to get that is to use the generic version of GetComponent: