2D Grid Question

I found this post which helped me a great deal -

http://answers.unity3d.com/questions/262419/2d-grid-accessing-in-different-gameobject.html?sort=oldest

though when I implement this code everything works apart from the mouse over part. I placed a Debug.Log in there and it definitely is not recording the mouse over part?! Any answers?

There are no errors in the code and the names are all spelt correctly i'm lost!

Any help would be appreciated!

     //WhateverGrid.js
     var gridData : DefenseGrid;
 
     function Start(){
         gridData = GameObject.Find("Grid").GetComponent("DefenseGrid");
         
     }
 
     function OnMouseOver(){
         gridData.grid[1,2].renderer.material.color = Color.red;
         Debug.Log("Mouse over recorded");
         renderer.material.color = Color.red;
     }

 //DefenseGrid.js
 var grid : GameObject[,];
 var gridSizeX : int;
 var gridSizeY : int;
 var square : GameObject;
 
     function Start(){
         grid = new GameObject[gridSizeX, gridSizeY];
         for(var y : int = 0; y < gridSizeY; y++){
            for(var x : int = 0; x < gridSizeX; x++){
              var s : GameObject = GameObject.Instantiate(square, Vector3(transform.position.x-(x * (square.renderer.bounds.size.x)), transform.position.y+(y * (square.renderer.bounds.size.y)), transform.position.z), Quaternion.identity);
              grid[x, y] = s;
              Debug.Log("Yeah");
            }
         }
     }