Adding RequireComponent breaks script

After adding a RequireComponent directive to this script:

@script RequireComponent (Window)

class Menu extends MonoBehaviour{
	private var window : Window;
	
	function Start(){
		window = GetComponent(Window);
	}
	
	function OnGUI(){		
		Main.INSTANCE.executeSomeFunction();
	}
}

I can no longer access one of my singleton scripts. I get the error message:
'INSTANCE' is not a member of 'function(): void'.. Here is the singleton class:

class Main extends MonoBehaviour{
	static var INSTANCE : Main;

	function Start(){
		INSTANCE = FindObjectOfType(Main);
		setState(initialState);
	}
	
	function OnApplicationQuit(){
		INSTANCE = null;
	}
}

Why is this happening?

Using Main as the scripts name was causing issues after adding the RequireComponent line.