Can't set the width/height with createEmptyMovieClip?

programming flash
1

Doesn’t work


function thumbsMaker(imgURL, thumb_width, thumb_height, i, rows) {
	var thumbBG:MovieClip;
	var thumbContainer:MovieClip = createEmptyMovieClip("thumbContainer"+i, getNextHighestDepth());
	thumbContainer._x = 30;
	thumbContainer._y = 150;	
	var image:MovieClip = thumbContainer.createEmptyMovieClip("image",1);
	var thumbBG:MovieClip = thumbContainer.createEmptyMovieClip("thumbBG",0);
thumbBG._x = 50//testing
thumbBG._height = 40;
...more code
}

but i don’t see the height