Argument out of range?

Hey there, I've been trying to solve an Inventory System these past weeks.

(Most of this is from a tutorial, which I have expanded alot)

However there's a few bugs which causes an Argument is out of range to trigger.

This is specifically when I press the button which opens the Inventory.

Unity is not doing a great job in telling me what is causing this either.

I should add that I have a separate script for picking up items, but it does not work yet.

Here's alot of code (Gibberish if you will):

---

Specific lines it mentions in one such error.

 Item item = inventory [i];
 DrawInventory ();

---

Inventory.cs

 using UnityEngine;
 using UnityEngine.UI;
 using System.Collections;
 using System.Collections.Generic;
 using Sfs2X.Entities;
 using Sfs2X.Entities.Variables;
 using Sfs2X.Entities.Data;
 using Sfs2X.Requests;
 
 public class Inventory : MonoBehaviour
 {
     public int slotsX, slotsY;
     public GUISkin skin;
     public static List<Item> inventory = new List<Item>(); // List
     public List<Item> slots = new List<Item>(); // List
     private bool showInventory; // Show Inventory Bool
     public ItemDatabase database; // Item Database
     private bool showTooltip; // Tooltip Bool
     private string tooltip; // Tooltip String
     private bool dropItem; // Drop Item Bool
     private bool spawnItem;
     //private bool takeItem;
 
     private bool draggingItem;
     private Item draggedItem;
     private int prevIndex; // Previous Index
 
 
     // Use this for initialization
     public void Start()
     {
         database = GameObject.FindGameObjectWithTag("Item Database").GetComponent<ItemDatabase>();
         for (int i = 0; i < (slotsX * slotsY); i++)
         {
             inventory.Add(new Item());
         }
     }
 
     void Update() // Show the inventory if we press the key I
     {
         if (Input.GetButtonDown("Inventory"))
         {
             showInventory = !showInventory;
 
             ItemDatabase.FetchItemBySlug("potion");
         }
     }
 
     void OnGUI() // Tooltip, Draw Inventory and Item Drag Icon
     {
         tooltip = "";
         GUI.skin = skin;
         if (showInventory)
         {
             DrawInventory ();
             if (showTooltip)
             {
                 GUI.Box(new Rect(Event.current.mousePosition.x + 15, Event.current.mousePosition.y + 10, 200, 200), tooltip, skin.GetStyle("Tooltip"));
                 showTooltip = false;
             }
         }
         if (draggingItem)
         {
             GUI.DrawTexture(new Rect(Event.current.mousePosition.x, Event.current.mousePosition.y, 50, 50), draggedItem.itemIcon);
         }
         if (dropItem) {
             
                 DropItem (this.draggedItem);
             }
         }
 
 
     void DrawInventory() // Draw the inventory, allow dragging and dropping of items.
     {
         Event e = Event.current;
         int i = 0;
         for (int y = 0; y < slotsY; y++) {
             for (int x = 0; x < slotsX; x++) {
                 Rect slotRect = new Rect (x * (45 + 12), y * (45 + 12), 57, 57);
                 GUI.Box (slotRect, "", skin.GetStyle ("Inventory"));
                 Item item = inventory [i];
                 if (item.itemName != null) 
                 {
                     if (item.itemIcon != null) GUI.DrawTexture (slotRect, inventory [i].itemIcon);
                     if (item.itemquantity > 1) {
                         GUI.Label (slotRect, inventory [i].itemquantity.ToString ());
                     }
                     if (slotRect.Contains (e.mousePosition)) {
                         tooltip = CreateTooltip (inventory [i]);
                         showTooltip = true;
                         if (e.button == 0 && e.type == EventType.mouseDrag && !draggingItem) {
                             draggingItem = true;
                             prevIndex = i;
                             draggedItem = inventory [i];
                             inventory [i] = new Item ();
                         }
                         if (e.type == EventType.mouseUp && draggingItem) {
                             inventory [prevIndex] = inventory [i];
                             inventory [i] = draggedItem;
                             draggingItem = false;
                             draggedItem = null;
                         }
                         if (e.isMouse && e.type == EventType.mouseDown && e.button == 1)
                         if (item.itemType == Item.ItemType.Consumable) {
                             UseConsumable (inventory [i], i);
                         }
                     }
                     i++;
                 } else {
                     if (slotRect.Contains (e.mousePosition)) {
                         if (e.type == EventType.mouseUp && draggingItem) {
                             inventory [i] = draggedItem;
                             draggingItem = false;
                             draggedItem = null;
                             
                         }
                     } else if (e.type == EventType.mouseUp && draggingItem && spawnItem == false && (e.mousePosition.x > slotsX * (45 + 12) || e.mousePosition.y > slotsX * (45 + 12))) {
                         inventory [prevIndex] = new Item ();
                         dropItem = true;
                         spawnItem = true;
                         break;
                     }
                 }
                             if (tooltip == "") {
                                 showTooltip = false;
                             }
                             i++;
                         }
                     }
                 }
             
         
     string CreateTooltip(Item item)
     {
         tooltip = "";
         if (item.itemType == Item.ItemType.Weapon)
         {
             tooltip += "<color=#FFFFFF>" + item.itemName + "</color>\n\n" + "<color=#FFFFFF>" + item.itemDamage + " Damage" + "</color>\n\n" + item.itemDesc + "\n" + item.itemType + "\n"; // Draw Tooltip, Text Color and Attributes
         }
         if (item.itemType == Item.ItemType.Consumable)
         {
             tooltip += "<color=#FFFFFF>" + item.itemName + "</color>\n\n" + "<color=#FFFFFF>" + "</color>\n\n" + item.itemDesc + "\n" + item.itemType + "\n"; // Draw Tooltip, Text Color and Attributes
         }
         if (item.itemType == Item.ItemType.Quest)
         {
             tooltip += "<color=#FFFFFF>" + item.itemName + "</color>\n\n" + "<color=#FFFFFF>" + "</color>\n\n" + item.itemDesc + "\n" + item.itemType + "\n"; // Draw Tooltip, Text Color and Attributes
         }
         return tooltip;
     }
 
 
 
     public void RemoveItem(int id) // Remove Item
     {
         for (int i = 0; i < inventory.Count; i++)
         {
             if (inventory[i].itemID == id)
             {
                 inventory[i] = new Item();
                 break;
             }
         }
     }
 
     void AddItem(int id) // Add Item
     {
         for (int i = 0; i < inventory.Count; i++)
         {
             if (inventory[i].itemName == null)
             {
                 for (int j = 0; j < database.items.Count; j++)
                 {
                     if (database.items[j].itemID == id)
                     {
                         inventory[i] = database.items[j];
                     }
                 }
                 break;
             }
         }
     }
 
     void DropItem(Item item) //Drop Item
     {
         if (spawnItem == true) {
             Debug.Log (item.itemName + " dropped");
 
             //Here goes the send mmoitem to server code..
             //The position to spawn;  newVector2(NetworkLogin.GetLocalPlayer().transform.position.x,            NetworkLogin.GetLocalPlayer().transform.position.y)
 
 
             ISFSObject objt = SFSObject.NewInstance ();
 
             objt.PutUtfString ("name", item.itemName);
             objt.PutInt ("id", item.itemID);
             objt.PutUtfString ("desc", item.itemDesc);
             objt.PutInt ("damage", item.itemDamage);
             objt.PutInt ("speed", item.itemSpeed);
             objt.PutInt ("health", item.itemRestore);
             objt.PutUtfString ("type", item.itemType.ToString ());
             objt.PutBool ("stackable", item.itemstackable);
             objt.PutInt ("rarity", item.itemrarity);
             objt.PutUtfString ("slug", item.itemslug);
 
             objt.PutFloat ("x", NetworkLogin.GetLocalPlayer ().transform.position.x);
             objt.PutFloat ("y", NetworkLogin.GetLocalPlayer ().transform.position.y);
 
             SFS2X_Connect.sfs.Send (new ExtensionRequest ("SpawnMMOItem", objt));
 
             spawnItem = false;
         }
         draggingItem = false;
         dropItem = false;
         draggedItem = null;
         
     }
 
 
     public bool InventoryContains(int id)
     {
         foreach (Item item in inventory)
             if (item.itemID == id) return true;
         return false;
 
     }
 
 
     private void UseConsumable(Item item, int slot)
     {
         if(item.itemquantity > 1)
         {
             item.itemquantity--;
             Debug.Log("You used " + item.itemName + " and gained " + item.itemRestore + " health.");
         }
 
         else
         {
             inventory[slot] = new Item();
             Debug.Log("You used " + item.itemName + " and gained " + item.itemRestore + " health.");
         }
 
     }
 
 }