attachMovie and clear interval

programming flash
1

Hi everyone,
Im using attachMovie to load movieclips dynamically on the stage.
this works fine except that there is always an extra movieClip on the top, left corner of the stage.

I am using a set interval to place the mc’s on stage at regular intervals.

I also have a clearInterval that is not getting triggered. I got the code for this from the flash help files.

my code for attachMovie is as follows:


var intervalId:Number;
 
function placeFrogs():Void {
 this.attachMovie("frog_id", "frog_mc", this.getNextHighestDepth());
 this.frog_mc._x = random (500)+ 10;
 this.frog_mc._y = random (450)+ 10;
}
 
//put the placefrogs function inside another function which will be triggered
//by the setInterval
 
function timerPlaceFrogs():Void{
 placeFrogs();
}
 
 
//this loads the frog_mc on the stage after approx 2 secs
 
function beginInterval():Void {
if(intervalId != null) {
 trace("clearInterval");
 clearInterval(intervalId);
 }

 intervalId = setInterval(timerPlaceFrogs, 1800);
}
beginInterval();

any pointers on where I am going wrong?
Thank you .