setMask() for loadMovie possible?

programming flash
1

I tried to apply setMask() method on loadMovie() - it not works or make I someth wrong?

loadMovie (“main_anim.swf”, container_mc_main);
container_mc_main._x = 477.8;
container_mc_main._y = 49.5;
trace ("container_mc_main.getDepth() = " + container_mc_main.getDepth ());
circleMask_mc._x = container_mc_main._x;
circleMask_mc._y = container_mc_main._y;
trace ("circleMask_mc.getDepth() = " + circleMask_mc.getDepth ())
container_mc_main.setMask (circleMask_mc);