Question : problem: loading sub external swf

i have main.swf which loads usa.swf from sub folder "countries", and it loads it perfectly

var ldr:Loader = new Loader();
var url:URLRequest = new URLRequest("countries/usa.swf");
ldr.load(url)
addChild(ldr)

same technique, the usa.swf loads external swf in the same folder. and it loads it perfectly

var usa_ldr:Loader = new Loader();
var usa_url:URLRequest = new URLRequest("flag.swf");
usa_ldr.load(usa_url)
addChild(usa_ldr)

but, when i test from main.swf, i get this error:
Error #2044: Unhandled IOErrorEvent:. text=Error #2035: URL Not Found.

var url:URLRequest = new URLRequest("countries/usa.swf");
var usa_url:URLRequest = new URLRequest("./flag.swf");

not one is working

urgent please

Answer : problem: loading sub external swf

var usa_ldr:Loader = new Loader();
var usa_url:URLRequest = new URLRequest("countries/flag.swf");
usa_ldr.load(usa_url)
addChild(usa_ldr)

the child added to main takes on main's location.