Frame 0

Where does your playhead lie when you finish loading a movieclip.
Answer: Frame 0. Try loading in a swf via MovieClipLoader. In the onLoadComplete, make the mc stop playing: mc.stop();

Now, if you try to target something that you have put on stage in frame 1, you will get a null reference. Because at this point, the playhead is not in frame 1 yet. So if you want to stop your loaded swf from playing,

perhaps try
1) gotoAndStop(1) (I have found this not to work sometimes),

2) do a two-liner:
mc.nextFrame();
mc.stop();

3) put a stop frame in the original fla.

Make sure you charge your client extra for knowing stuff like this (jk!)