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 t$$anonymous$$s for a w$$anonymous$$le 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.