Scale sprite problem

I tried to scale my background sprite to the screen resolution, but it doesn't work.
What am I doing wrong?

Code (CSharp):

1. using UnityEngine;
2. using System.Collections;
3.  
4. public class ScaleBackground : MonoBehaviour {
5.  
6.     GameObject Background;
7.  
8.     // Use this for initialization
9.     void Start()
10.     {
11.         Background = GameObject.Find("Background");
12.  
13.         float windowWidth = Screen.width;
14.         float windowHeight = Screen.height;
15.  
16.         float spriteWidth = Background.transform.GetComponent<BoxCollider2D>().size.x * 100;
17.         float spriteHeight = Background.transform.GetComponent<BoxCollider2D>().size.y * 100;
18.  
19.         float backgroundWidth = windowWidth / spriteWidth;
20.         float backgroundHeight = windowHeight / spriteHeight;
21.  
22.         // Scale Sprite
23.         Background.transform.localScale = new Vector3(backgroundWidth, backgroundHeight, 0);
24.     }
25.     // Update is called once per frame
26.     void Update () {
27.    
28.     }
29. }
30.  

 

Have a look at an older post I did about, more or less, the same issue:
http://forum.unity3d.com/threads/scrolling-background-2d-sprite-background.301931/#post-1984247