My flex 4 program has a button controlled animation. it works but is playing once once, if i click the button again it doesnt work...

Question

i'm pasting part of the the code here

    <s:Parallel id="panelIn" target="{back}" >
        <mx:Move xTo="-400" duration="2500" easingFunction="Bounce.easeIn"/>
        <s:Fade   alphaFrom="1.0" alphaTo="0.0"  duration="2500" />
    </s:Parallel>   

this is the animation

protected function button1_clickHandler(event:MouseEvent):void
        {
            panelIn.play();
            back.visible="false";
            myVS.selectedIndex=0;
        }
        protected function adminbutton_clickHandler(event:MouseEvent):void
        {
            myVS.selectedIndex=0;
            back.visible="true"
            panelOut.play();

        }

and this is the function