OnGUI() works on Editor but not on Android Device

It's pretty simple. I'm trying to get Native GUI to make a Menu screen of sorts. And on Editor and Game it works perfectly, but when I export it on the device, it doesn't show.

The script is attached to the Camera, and there's only a Cube in front of it having no other script.

My script is as follows:

 using UnityEngine;
 using System.Collections;
 
 public class newmenu : MonoBehaviour {
     private Rect b;

     void Start () {
         
         int w = Screen.width;
         int h = Screen.height;
         
         //name = new Rect ( px ,py ,bh, bw)
         b = new Rect (w -3*w/4, h - 4*h/5 , 2*w/4, h / 10);
         }
     
     void OnGUI(){
         
         if (GUI.Button (b, "Begin")) {
             Application.LoadLevel("SolidWhite");
         }                        
     }
 }

What am I doing wrong? Even Canvas Buttons do the same thing! OnGui works fine on the other scenes, just this one!