instantiate a cube at a position by read from xml file

hello, While reading from the xml file,instantiating of start and dest is not visible(it shows up when z cooedinate value changed to -2) while without xml reading it works fine(for openf == 0).Iam really not able to figure out what is the problem.Please help

void Start()

 {
     if (PlayerPrefs.GetInt("openf") == 0)
     {
         size.x = PlayerPrefs.GetInt("size_l");
         size.y = PlayerPrefs.GetInt("size_b");
         parent_nodes = new nodes[(int)size.x * (int)size.y];
         grid_arr = new Transform[(int)size.x, (int)size.y];//array to refference to grids created
         for (int x = 0; x < size.x; x++)//creating grids
         {
             for (int z = 0; z < size.y; z++)
             {
                 Transform newcel;
                 newcel = (Transform)Instantiate(cellprefab, new Vector3(x, z, 0), Quaternion.identity);
                 newcel.name = (newcel.position.x.ToString() + newcel.position.y.ToString());
                 newcel.parent = transform;
                 grid_arr[x, z] = newcel;
             }
         }
         creategrid();
     }
     else 
     {

         string xml = PlayerPrefs.GetString("xmlfile");
         int x = 0, y = 0;
         file_path = PlayerPrefs.GetString("file");
         if (file_path != "")
         {
             XmlDocument xmlDoc = new XmlDocument();
             xmlDoc.LoadXml(xml);
             XmlElement root = xmlDoc.DocumentElement;
             if (root.HasAttributes)
             {
                 int.TryParse(root.GetAttribute("size_x"), out x);
                 int.TryParse(root.GetAttribute("size_y"), out y);
                 size.x = x;
                 size.y = y;
                 parent_nodes = new nodes[(int)size.x * (int)size.y];
                 grid_arr = new Transform[(int)size.x, (int)size.y];//array to refference to grids created
             }
             
             XmlNodeList grds = xmlDoc.GetElementsByTagName("Grid");
             bool f = false;
             foreach (XmlNode nd in grds)
             {
                 XmlElement elm = (XmlElement)nd;
                 if (elm.GetElementsByTagName("name")[0].InnerText == "block")
                 {
                     int.TryParse(elm.GetElementsByTagName("X")[0].InnerText, out x);
                     int.TryParse(elm.GetElementsByTagName("Y")[0].InnerText, out y);
                     b = (Transform)Instantiate(block, new Vector3(x, y, -1), Quaternion.identity);
                     b.parent = transform;
                     b.name = "block";
                     grid_arr[x, y] = b;
                 }
                 else
                 {
                     int.TryParse(elm.GetElementsByTagName("X")[0].InnerText, out x);
                     int.TryParse(elm.GetElementsByTagName("Y")[0].InnerText, out y);
                     b = (Transform)Instantiate(cellprefab, new Vector3(x, y, -1), Quaternion.identity);
                     b.parent = transform;
                     b.name = x.ToString()+y.ToString();
                     grid_arr[x, y] = b;
                 }
             }
 
         }
         else
         {
             MessageBox.Show("!!!Corrupted XML file \n \t or\n Invalid XML file...");
         }
         creategrid();
     }
 }

void creategrid()

 {
     Camera.main.transform.position = new Vector3(grid_arr[(int)(size.x / 2), (int)(size.y / 2)].position.x, grid_arr[(int)(size.x / 2), (int)(size.y / 2)].position.y, -5);//scaling to the view
     /////////////////////////////////////////Set camera view///////////////////////////////////////////////
     bool f = false;
     for (int i = 0; i < size.x; i++)//creating grids
     {
         for (int j = 0; j < size.y; j++)
         {
             if (grid_arr[i, j].name != "block")
             {
                 if (f == false)
                 {
                     start = (Transform)Instantiate(start, new Vector3(i, j, -1), Quaternion.identity);
                     dest = (Transform)Instantiate(dest, new Vector3(i, j, -1), Quaternion.identity);
                     f = true;
                     break;
                 }
             }
         }
         if (f == true)
             break;
     }
     
     if (size.x > size.y)
     {
         Camera.main.orthographicSize = (size.x / 2) + 3f;//projecting the camera view to the game
     }
     else if (size.x < size.y)
     {
         Camera.main.orthographicSize = (size.y / 2) + 3f;//projecting the camera view to the game
     }
     else
     {
         Camera.main.orthographicSize = (size.x / 2) + 3f;//projecting the camera view to the game
     }

 }