Remove child

1

hi this i write a program . ciecle is display i using addchild and i using removechild for disappering circle.pls tell me
error no :1046 is come how can i clear this error

package
{

import flash.display.MovieClip;
import flash.display.Shape;


public class boxx extends MovieClip
{

	public function boxx():void
	{
	
		var box_1:box = new box();
		addChild(box_1);
		box_1.x = 170;
	}
	
	 mc_but.addEventListener(MouseEvent.CLICK, RemoveObject);
     public function RemoveObject(event:MouseEvent):void
	{
		//var box_1:box = new box();
		removeChild(box_1);
	}
}