You have to wait until the movie has been loaded into the level in order to modify its properties; you can use the [font=courier new]MovieClipLoader[/font] object to execute the code once that the movie is fully loaded. Example:
var listener = new Object();
listener.onLoadInit = function(target) {
target._x = 100;
};
var loader = new MovieClipLoader();
loader.addListener(listener);
loader.loadClip("overview_fb_v2_fr.swf", 5);