Flash 8 Actionscript Problems

I am attempting to write a code that will do the following:

  1. Produce a ball at the far right of the screen and have it move to the left.
  2. when the ball hits the left side of the screen, have it be replaced with a square moving in the opposite direction. (When the square hits the right side of the screen, it will change to the ball.)
  3. when the spacebar is hit, everything should reset itself to step 1.

My code looks like this (ball box are my movie clips):

function spawn(){
attachMovie(“ball”, “ball”, 1, {_x:550, _y:200});
};
function AI(){
ball._x -=1;
box._x +=1;
if(ball._x<=0){
removeMovieClip(ball);
attachMovie(“box”, “box”, 1, {_x:0, _y:200});
};
if(box._x>=550){
removeMovieClip(box);
attachMovieClip(ball);
};
};
function reset(){
if(Key.isDown(Key.SPACE)){
removeMovieClip(ball);
removeMovieClip(box);
attachMovie(“ball”, “ball”, 1, {_x:0, _y:200});
};
};
this.onEnterFrame = function(){
spawn();
AI();
reset();
};
What happens is that the ball forms at the correct location, but it does not move.
What am I doing wrong?