Load external as2 swf to main flash file as root and level0

hello.
first of all sorry about my english.
i have 2 flash files,one is mine (the main container) and one is a external swf.
i want to load the external swf to my container swf.
i write this code in my as2 container

— code inside the main timeline flash (mine flash) -----
*first of all i add a movie clip with instance name mc1 to the first layer

mc1._lockroot = true;
mc1.loadMovie("external.swf");
countdown = function(){
trace("ok");
}
countdownIt = setInterval(countdown,1000);

this code work fine in most of the cases but i found many swfs files that dosent work with this code and work with the **following **code instead :

loadMovieNum("external.swf",0);
countdown = function(){
trace("ok");
}
countdownIt = setInterval(countdown,1000);

i really try to use that code - BUT !!! -> if i use this code the external swf predominant my main swf code and all the rest of my code dosent work (like timer of trace)…

i am really need help here, i want to load movie like the second example and still run the timer trace function…
thank you guys !!!