Help with setFocus, please!

Hello;
I have a login page with 2 text boxes for user name and password, and a submit button.
All I want is to have the flashing cursor show up in the user name text area. The instance name for this is tUsername. It is in a movie clip called start. Below I am pasting the working login code, then most of the things I have tried with setFocus, help would be greatly appreciated, and thank you!

//the code below works fine
tError.autoSize = “right”;

_global.lvSend = new LoadVars();
_global.lvReceive = new LoadVars();

mcLogin.onRelease = function() {

lvSend.username = tUsername.text;
//Selection.setFocus(tUsername);


lvSend.password = tPassword.text;
lvSend.sendAndLoad("logincheck.php", lvReceive, "POST");

};

lvReceive.onLoad = function(success:Boolean) {
if (success) {
if (this.login == “success”) {
gotoAndPlay(“box_open”);
}else{
tError.text = “I’m sorry you did not enter valid login details”;
}
} else {
trace(“no reponse from server”);
}
};
_root.start.tUsername.selection.setFocus();

stop();

Here are some of the things I have tried so far above the onRelease function:

/*tUsername is the instance name of the text box

Selection.setFocus(_root.start.tUsername);
another try, with and without double quotes
Selection.setFocus(tUsername);
and
setFocus(_root.start.tUsername);
setFocus("_root.start.tUsername");
and again

Selection.setFocus(targetPath(this)+".tUsername");
Selection.setFocus(Selection.getFocus());
tUsername.onKillFocus = function() {
trace(Selection.getFocus());
trace(_name+"_root.start.tUsername");
Selection.setFocus("_root.start.tUsername");
}

if (this.tUsername.text !=null){
Selection.setFocus("_root.start.tUsername")
};

_root.start.tUsername.selection.setFocus();

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