java - Flex/Flash 4 ExternalInterface.call - trying to get a string from HTML to Actionscript

I need to obtain a string from HTML and put it into
Actionscript.

the
actionscript:

import
            flash.external.ExternalInterface;
protected function
            getUserName():void{
 var isAvailable:Boolean =
            ExternalInterface.available;
 var findUserName:String =
            "findUserName";
 if(isAvailable){
 var foundUserName:String =
            ExternalInterface.call(findUserName).toString();

            Alert.show(foundUserName);}}

the
javascript:

function
            findUserName() {
 var label =
            document.getElementById("username-label");
 if(label.value != ""){

            alert("the name in the box is: " + label.value);
 return
            label.value;}
 else
 return "nothing in the
            textbox";}}

the
JSP:

<%IUserSession userSession
            = SessionManager.getSession();%>

            name="userSession">
             name="userSession" property="userLoginId">
             width="10%" >
             value="" />

            

            

the
rendered HTML:

            align="right" width="10%">
             value="a-valid-username"
            />

when
the javascript execution hits

var
            label =
            document.getElementById("username-label");

a
null is returned and crashes, no alert shows no error message is shown.
I can
successfully do a search firefox DOM Inspector by "username-label"
(document.getElementById())

The only alert box
that pops up is the action script alert box and the contents are
blank.

firfox 3.5 windows, container
is Tomcat.

Please advise, and thank you in
advance.