DontDestroyOnLoad make errors

I have 2 scripts: first one is a script attached on all items of my scene and adds these on inventory; second one is the inventory system script attached on a gameobject with all inventory scripts (like database, toolips and go on).

Here the first:

 using UnityEngine;
 using System.Collections;
 using System.Collections.Generic;
 using System.IO;
 using System;
 using LitJson;
 
 public class ItemData : MonoBehaviour {
 
     public int ID;
 
     public enum itemIndex { MainEntranceKey = 0, Flashlight = 1, Medikit = 2}
     public itemIndex itemNameFromList;
 
     public float maxDistance = 5.0F;
 
     public Ray raycast;
 
     public bool pickedUp = false;
 
     private int itemID;
     private int itemsJsonIndex;
 
     public string itemState;
 
     private GameObject glob;
     private Inventory_System invDat;
     private Global_ItemInventory globScript;
     private PlayerInteractivity inter;
 
     private IEnumerator fetchInventory;
 
     void Start ()
     {
         pickedUp = false;
 
         fetchInventory = LoadItemDatabase ();
         StartCoroutine (fetchInventory);
     }
 
     IEnumerator LoadItemDatabase ()
     {
         glob = GameObject.Find ("GlobalParameters");
         while (glob == null) {
             yield return null;
         }
         globScript = glob.GetComponent <Global_ItemInventory> ();
         inter = GameObject.Find ("PlayerController").GetComponent<PlayerInteractivity> ();
         GameObject inv = GameObject.Find ("Inventory");
         while (inv == null) {
             yield return null;
         }
         Item_Database itemDat = inv.GetComponent<Item_Database> ();
         invDat = inv.GetComponent<Inventory_System> ();
         while (itemDat == null) {
             yield return null;
         }
         itemDat.itemList = JsonMapper.ToObject (File.ReadAllText (Application.dataPath + "/StreamingAssets/Items.json"));
         itemDat.items.Add (new Item ((int)itemDat.itemList [itemsJsonIndex] ["id"], itemDat.itemList [itemsJsonIndex] ["name"].ToString (), itemDat.itemList [itemsJsonIndex] ["desc"].ToString (), itemDat.itemList [itemsJsonIndex] ["raw"].ToString(), (int)itemDat.itemList [itemsJsonIndex] ["type"])); 
 
         if (itemNameFromList == itemIndex.MainEntranceKey) {
             itemsJsonIndex = 0;
         } else if (itemNameFromList == itemIndex.Flashlight) {
             itemsJsonIndex = 1;
         } else if (itemNameFromList == itemIndex.Medikit) {
             itemsJsonIndex = 2;
         }
 
         itemID = itemDat.items[itemsJsonIndex].ID;
         StopCoroutine (fetchInventory);
     }
 
     void Update ()
     {
         RaycastHit hit;
         raycast = Camera.main.ViewportPointToRay(new Vector3(0.5f, 0.5f, 0));
 
         if (Physics.Raycast (raycast, out hit, maxDistance) && hit.transform.name == name) 
         {
             Debug.DrawLine (raycast.origin, hit.point, Color.red);
 
             if (Input.GetButtonDown ("Interact") && inter.interactKeyEnable == true) 
             {
                 pickedUp = true;
                 TakeItem ();
             }
         }
     }
 
     void TakeItem ()
     {
         if (invDat.itemObj.Exists (x => x.ID == -1)) 
         {
             invDat.AddItem (itemID);
 
             ItemStat it = globScript.itemSt.Find (x => x.ID == ID);
             int k = globScript.itemSt.FindIndex (x => x.ID == ID);
 
             if (it != null) {
                 globScript.itemSt.Remove (it);
                 globScript.itemSt.Insert (k, (new ItemStat (ID, "Destroyed", name)));
             } else {
                 globScript.itemSt.Add (new ItemStat (ID, "Destroyed", name));
             }
 
             Destroy (this.gameObject, 0.0F);
         } 
         else 
         {
             Debug.Log ("FULL");
         }
     }
 }
 

And the second:

 using UnityEngine;
 using UnityEngine.UI;
 using System.Collections;
 using System.Collections.Generic;
 
 public class Inventory_System : MonoBehaviour {
 
     public int maxSlots;
 
     public GameObject inventorySlot;
     public GameObject inventoryIcon;
 
     public List<Item> itemObj = new List<Item> ();
     public List<GameObject> slots = new List<GameObject> ();
 
     private GameObject inventoryPanel;
     private GameObject slotPanel;
     private Item_Database database;
 
     void Start () 
     {
         database = GetComponent<Item_Database> ();
 
         inventoryPanel = GameObject.Find ("InvPanel");
         slotPanel = inventoryPanel.transform.FindChild ("InvSlot").gameObject;
 
         for (int i = 0; i < maxSlots; i++) 
         {
             itemObj.Add (new Item());
             slots.Add (Instantiate (inventorySlot));
             slots [i].transform.SetParent (slotPanel.transform);
             slots [i].transform.localScale = new Vector3 (1, 1, 1);
         }
     }
 
     public void AddItem(int id)
     {
         Item itemToAdd = database.FetchItemByID (id);
         for (int i = 0; i < itemObj.Count; i++) 
         {
             if (itemObj [i].ID == -1) 
             {
                 itemObj [i] = itemToAdd;
                 GameObject objects = Instantiate (inventoryIcon);
                 objects.GetComponent<SelectionTool> ().item = itemToAdd;
                 objects.transform.SetParent (slots[i].transform);
                 objects.transform.localScale = new Vector3 (1, 1, 1);
                 objects.transform.localPosition = Vector2.zero;
                 objects.GetComponent<Image> ().sprite = itemToAdd.Sprite;
                 slots [i].name = itemObj [i].Name;
                 objects.name = itemToAdd.Name;
                 break;
             }
         }
     }
 
     public void LoadData(int max, int[] id)
     {
         maxSlots = max;
 
         for (int i = 0; i < maxSlots; i++) 
         {
             if (id [i] != -1) 
             {
                 AddItem (id [i]);
             }
         }
     }
 }

If I add the DontDestroyOnLoad () function in the inventory system script (and I would to do that), the first script ItemData gives me this error:

ArgumentOutOfRangeException: Argument is out of range. Parameter name: index System.Collections.Generic.List`1[Item].get_Item (Int32 index) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Collections.Generic/List.cs:633) ItemData+c__Iterator8.MoveNext () (at Assets/Script/ItemData.cs:69) UnityEngine.MonoBehaviour:StartCoroutine(IEnumerator) ItemData:Start() (at Assets/Script/ItemData.cs:38)

But if I don't put that function, these scripts works very well, but I need that function...

What am I doing wrong?