Instantiate Error test

NewBehaviourScript.cs

using UnityEngine;
using System.Collections;

public class NewBehaviourScript : MonoBehaviour {

	public GameObject enemyPrefab;

	// Use this for initialization
	void Start ()
	{
		// Create enemy
		GameObject enemyObject = (GameObject)Instantiate(enemyPrefab);
		enemyObject.transform.position = new Vector3(0.0f, 1.0f, 0.0f);
	}
	
	// Update is called once per frame
	void Update () {
	
	}
}