IDE :: Loading PlayerMenu - RangeError When Index Specified

I simply load a playermenu from the library and then attach the whole player_menu to the stage. When doing it with addChild it works, however when I specify a index it reports that error. (I need to use it because i want to control the indexing of movieclips). I am just not able to add a child with addChildAt, whats the error here?

PHP Code:
//menuvar player_menu:MovieClip = new MovieClip();
var player_menu_sub:playermenu = new playermenu();
player_menu.addChild(player_menu_sub);player_menu.y=174;
this.addChildAt(player_menu, 6);
output.text=this.getChildIndex(player_menu).toString();