Action Script Problem (Flash CS4)

programming flash
1

[FONT=Calibri][SIZE=3]Hey guys, I’m a bit stuck, I recently found this cool typewriter effect which works fine. However, for some reason I can only use it once, it won’t let me use it in any other scene without having problems. Anyone know why?[/SIZE][/FONT]

 
var str:String = "Testing testing testing tesing testing testing";
 
var timer:Timer = new Timer(20);
 
var i:uint =0;
 
timer.addEventListener(TimerEvent.TIMER,gotime);
 
timer.start();
 
function gotime(e:TimerEvent){
 textbox_txt.appendText(str.charAt(i));
 i++;
 if(i>=str.length){
  timer.stop();
  }
 }