Error when trying to save inventory with array.

I am using http://www.unifycommunity.com/wiki/index.php?title=Save_and_Load_from_XML to save and load.

i have an inventory with array. That is class that contains items vars. This form Inv_Inventory from Player:

 class InventoryItem
 {
 
     var worldObject: GameObject;
     var itemIcon: Texture;
     var itemName : String;
     var itemDescription : String;
     var Stack : int;
     var MaxStack : int;
 
 }

This From SaveLoad:

  if (GUI.Button(_Save,"Save")) {
             
       GUI.Label(_SaveMSG,"Saving to: "+_FileLocation);
       //Debug.Log("SaveLoadXML: sanity check:"+ _Player.transform.position.x);
       var plr = gameObject.Find("Player");
 var invScrpt = plr.GetComponent(Inv_Inventory);
 
       myData._iUser.x = _Player.transform.position.x;
       myData._iUser.y = _Player.transform.position.y;
       myData._iUser.z = _Player.transform.position.z;
       myData._iUser.name = _PlayerName;   
       
         for( var j = 0; j < myData._iUser.inventory.length; j ++ )
     {
         for( var s = 0; s < myData._iUser.inventory[j].length; s ++ )
         {
       
       for( var i = 0; i < invScrpt.inventory.length; i ++ )
     {
         for( var k = 0; k < invScrpt.inventory[i].length; k ++ )
         {
         if (invScrpt.inventory[i][k] != null)
         {
         myData._iUser.inventory[j][s] = invScrpt.inventory[i][k];
         }
         }
     }
     }
     }
       // Time to creat our XML!
       _data = SerializeObject(myData);
       // This is the final resulting XML from the serialization process
       CreateXML();
       Debug.Log(_data);
    }

Like That i am trying to save Inventory Array to file.

But when i click save and have item in inventory i have this error.

InvalidOperationException: The type of the argument object 'Inv_Inventory.InventoryItem' is not primitive.

Help me plz guys. I don't know what to do.