Fading in externally loaded images

Alright for some reason i’m having some trouble with this little bit of actionscript. I’ve never been great at it so i need a little nudge every once in a while.

Anyway, i’ve got an image gallery that is loading external images into empty movieclips that are on the stage. This all works fine. What i’m trying to do is give the larger image (medium_mc) a nice fade in once it loads. This is the script that i’ve got so far:

MovieClip.prototype.loadPic = function(pic){
	medium_mc._alpha = 0;
	medium_mc.loadMovie(pic);
	medium_mc.onEnterFrame = function(){
		var t = medium_mc.getBytesTotal(), l = medium_mc.getBytesLoaded();
		if (t != 0 && l == t){
			medium_mc._alpha += 5;
		}
		if (medium_mc._alpha>90) {
                medium_mc._alpha = 100;
                delete this.onEnterFrame;
        }
	}
};

What’s happening with this is the image is staying invisible and never fades up.

So hopefully one of you awesome guys will glance over that and see what i’m doing. Thanks in advance.