Need help understanding removeChild

I am creating multiple instances of a movie class with the same variable name. The movie is then added random on the stage with a tween. On a mouse handler click, i want to remove the movie from the stage.

I am getting error -

ArgumentError: Error #2025: The supplied DisplayObject must be a child of the caller.
at flash.display::DisplayObjectContainer/removeChild()
at Untitled_fla::MainTimeline/removeBlock()
What am I doing wrong?

import gs.TweenLite;
import flash.utils.*;

var block:block_mc;

var myTimer:Timer = new Timer(1000, 15);

myTimer.addEventListener(TimerEvent.TIMER, run); 

function run(event:TimerEvent):void {
    block = new block_mc;
    block.x = Math.round(Math.random() * 400); 
    block.y = Math.round(Math.random() * 400); 
    block.alpha = 0;
block.mouseChildren = false;
    stage.addChild(block);, 1, {alpha:1});
    stage.addEventListener(MouseEvent.CLICK, removeBlock); 

function removeBlock(event:MouseEvent):void{