Beh, dovrebbe essere:

codice:
barra._visible = 0;
function preloadIMG() {
    var car = holder.getBytesLoaded();
    var tot = holder.getBytesTotal();
    var perc = Math.round((car/tot)*100);
    if (car == tot && car>4) {
        clearInterval(prel);
        barra._visible = 0;
        holder._alpha = 100;
        return;
    }
    barra._xscale = perc;
    barra._visible = 1;
}
stop();
loadIMG(this.img);// variabile esterna