[away3d] load obj file

[andrew barry]

I cant load a obj file and i followed the tutorial 
http://www.charglerode.com/blog/?p=164
I am using flashbuilder4 AS3 project.

TypeError: Error #1009: Cannot access a property or method of a null
object reference.
      at away3d.loaders::Loader3D/loadTextures()[C:\HOME
\08659543\flashBuilder_3D\away3d_3_6_0\src\away3d\loaders\Loader3D.as:
486]


      public class mytest5 extends MovieClip
      {
            protected var _scene:Scene3D;
            protected var _view:View3D;
            protected var _camera:Camera3D;
            protected var _light:DirectionalLight3D;
            protected var _loader:Loader3D;
            protected var _mesh:Object3D;

            public function mytest5()
            {
                  initAway();
            }

            private function initAway():void
            {
                  _camera =  new Camera3D({zoom:20, focus:30, x:100, y:
50, z:-500});

                  _scene = new Scene3D();

            //      _light = new DirectionalLight3D();
            //      _scene.addChild( _light );

                  _view = new View3D( { x:stage.stageWidth / 2,
y:stage.stageHeight / 2, scene:_scene, camera:_camera,
renderer:Renderer.CORRECT_Z_ORDER } );
                  addChild( _view );

                  _loader = Obj.load( "m4_sherman.obj", { scaling:10,
bothsides:true } );
                  _loader.addOnSuccess( onObjLoad );
            }

            private function onObjLoad( e:Loader3DEvent ):void
            {
                  _mesh = e.loader.handle;
                  _mesh.scaleX = -1;

                  _scene.addChild( _mesh );

                  addEventListener( Event.ENTER_FRAME, onRender );
            }

            private function onRender( e:Event ):void
            {
                  _mesh.rotationY += 1;

                  _view.render();
            }