Object reference not set to an instance of an object

Questions & Answers
1

Code

#pragma strict

function Update ()
{
	if (Input.GetMouseButtonDown(0))
	{
		Hit();
	}
}

function Hit()
{
	var ray = Camera.main.ScreenPointToRay (Input.mousePosition);
	var hit : RaycastHit;
	if (Physics.Raycast (ray, hit, 100)) {
		hit.transform.BroadcastMessage("Drop");
		Debug.DrawLine (ray.origin, hit.point);
	}
}
2

Is your camera tagged as “MainCamera”? If not, Camera.main will be null.

Look here.