Weird NullReferenceException

i’m working on a new menu and i need the buttons to become uninteractable when the player hasn’t unlocked the levels yet. I’ve had a script for this for a while now and in the old scene/menu it works perfectly and gives no errors but in the new scene/menu it gives a NullReferenceException: Object reference not set to an instance of an object on line 27 and none of the buttons become uninteractable.

I’m using the new unity 4.6

Here is the script:

   using UnityEngine;
    using System.Collections;
    using UnityEngine.UI;
    
    public class LevelSelectScript : MonoBehaviour {  
    	private int levelIndex; 
    	GameObject Button;
    	void  Start (){
    				CheckLockedLevels(); 
    	}
    	
    	//Level to load on button click.
    	public void Selectlevel(string Level){
    		Application.LoadLevel("TransferData"+Level); //load the level			
    	}
    
    	//Checks if the buttons are interactable or not
    	void  CheckLockedLevels (){
    	for(int j = 1; j < LockLevel.levels; j++){
    	levelIndex = (j+1);
    	if((PlayerPrefs.GetInt("level"+levelIndex.ToString()))==1){
    				Button = GameObject.Find("Level"+(j+1));
    				Button.GetComponent<Button>().interactable = true;
    			}
    			if((PlayerPrefs.GetInt("level"+levelIndex.ToString()))==0){
    				Button = GameObject.Find("Level"+(j+1));
    				Button.GetComponent<Button>().interactable = false;
    		}
    	}
    }
    }

The new buttons have the same names as the old buttons in the editor.

try to add an if statement to ask, if the button != null

if(Button != null){
     Button.GetComponent<Button>().interactable = false;
}

hope it works