Collision not working

So I made a simple script that takes you to the main menu when an enemy collides with you. I got it to work and it had 0 errors. Everything worked perfectly. Then I saved my project, saved my scene and closed Unity. However when I reopen my project, the script doesn't work. At all. Why does Unity do this? It's not the first time this happens to me. At first it works but then when I restart Unity it doesn't work anymore...

Here's my code...

EDIT: Remember there are 0 errors and the scene is in the build settings. Nothing from the script was changed at all. Yet it stopped working all of the sudden.

 #pragma strict
 
 function OnCollisionEnter (collision : Collision) {
     if (collision.gameObject.tag == "Ghost") {
     Application.LoadLevel("intro test");
     }
         }