Please help. Can't add script problem.

I have a really big problem with this script. I did an other one before and it worked. this time is this problem that i can't add script. Someone please help. Thank you in advance.

 using UnityEngine;
 using System.Collections;
 using System.Collections.Generic;
 
 
 public class NewBehaviourScript : MonoBehaviour {
     public List<Item> inventory = new List<Item>();
     private ItemDatabase database;
 
 
     // Use this for initialization
     void Start () {
         database = GameObject.FindGameObjectWithTag("Item Database").GetComponent<ItemDatabase>();
         print (database.items [0].itemName);
     }
     
     // Update is called once per frame
     void Update () {
     
     }
 }