loadMovie becomes inactive

I have several photos being loaded via XML. No problem. Everything loads great. However, after loading the initial thumbnail into a mc (tn2) and rolling over it (which works) it becomes inactive. I can’t get a onRollOut function to work?

//initial load using xml string

thumb2off = _global.allItems[_global.x].thumb2off;
this.tn2.loadMovie(thumb2off); 
thumb2on = _global.allItems[_global.x].thumb2on; //loads fine


// rollover

this.tn2.onRollOver = function(){
tn2.loadMovie(thumb2on);
} // works

/// rollout 
tn2.onRollOut = function(){
this.loadMovie(thumb2off);
} // this does not work, nor does any other function (onPress, etc)

Why does the button become inactive after I load a new movie into the empty clip (tn2)?