Instantiating prefabs: "The object of type GameObject has been destroyed".

I am using this code to equip items on the player:

     //Equipping items on the character's model
     public void EquipItems()
       {
         //runs through each location where the items will be equipped on the player character model
         for (int i = 0; i < 5; i++)
         {
             //if the equip location exists
             if (itemLocation [i] != null)
             {
                 //destroys any existing equipped items if they don't match the newly-equipped items
                 foreach (Transform child in itemLocation[i].transform)
                 {
                     if (child != null)
                     {
                         if (child.gameObject.name != equippedItems[i].itemPrefab.name && child.gameObject.tag == "Item")
                         {
                             GameObject.Destroy(child.gameObject);
                         }
                     }
                 }
                 //places the new items in their locations
                 equippedItemsClones[i] = Instantiate (equippedItems [i].itemPrefab, itemLocation[i].transform.position, itemLocation[i].transform.rotation) as GameObject;
                 equippedItemsClones[i].transform.parent = itemLocation[i].transform;
                 Debug.Log("instantiating " + equippedItems[i].itemName);
             }
         }
   }

But, when I run it, I pick up an item from the ground, try to equip it, and get shown this error message:

MissingReferenceException: The object of type 'GameObject' has been destroyed but you are still trying to access it. Your script should either check if it is null or you should not destroy the object. UnityEngine.Object.Internal_InstantiateSingle (UnityEngine.Object data, Vector3 pos, Quaternion rot) (at C:/BuildAgent/work/d63dfc6385190b60/artifacts/EditorGenerated/UnityEngineObject.cs:74) UnityEngine.Object.Instantiate (UnityEngine.Object original, Vector3 position, Quaternion rotation) (at C:/BuildAgent/work/d63dfc6385190b60/artifacts/EditorGenerated/UnityEngineObject.cs:84) CharacterClass.EquipItems () (at Assets/scripts/Classes/CharacterClass.cs:94) InventoryScript.Update () (at Assets/scripts/GUIScripts/InventoryScripts/InventoryScript.cs:63)

I don't know what's gone wrong.