Question about the famous this._lockroot=true;

Hi everybody
I try to load a swf through a Loadmovie function. the swf loads but without animation. After research, I found out that to get the animation I have to put the following
[COLOR=blue]this._lockroot=true; [/COLOR][COLOR=black]in the first frame of the main stage. But on this frame I already have [/COLOR]

[COLOR=green]stop();
_root.captions._visible = 0;[/COLOR]
[COLOR=#008000][COLOR=black]When I add[/COLOR] [/COLOR][COLOR=black]the this._lockroot=true, nothing happen, my swf is still without animation.[/COLOR]
I am not an expert… can sbdy help?
Thanks