Function in a Function

[Gloo pot]

I have this peice of code and all of it works except the bolded part, i cant figure out why, i thought it might have somthing to do with it being inside another function.

function RunBubble() {
	var i;
	for (i=0; i<BubbleCount; i++) {
		if (_root.BubbleArray[i] == 1) {
			if (_root["BubbleArray"+i].num == 1) {
				_root["BubbleArray"+i]._y -= 5;
				if (_root["BubbleArray"+i]._y<-10) {
					_root["BubbleArray"+i].removeMovieClip();
					_root.BubbleArray[i] = 0;
				}
				_root["BubbleArray"+i].onRollOver = function() {
					_root["BubbleArray"+i].removeMovieClip();
					_root.BubbleArray[i] = 0;
				};
			}
		}
	}
}

I know all the other stuff works because the bubbles move upwards and are removed at the top of the stage.