Wallpaper change code not working

The line wallpaperManager.setResource(R.drawable.wall1); gives error (red line on R.drawable.wall1)

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.wallpaper_set);

    bSet = (Button) findViewById(R.id.bSetWall);

    bSet.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            WallpaperManager wallpaperManager = WallpaperManager.getInstance(WallpaperSet.this);
            try {
                wallpaperManager.setResource(R.drawable.wall1);
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    });
}