Elastic no worky in flash 8

    x = -this._x + centerx ;
    y = -this._y + centery ;
    
    xp = xp * inertia + x*k ;
    yp = yp * inertia + y*k ;

    _x += xp ;
    _y += yp ;

this code works if i publish the swf as flash 6 or earlier… does anybody know an elastic script that works in flash 8???