Cant read from javascript

programming flash
1

Actionscript Code

 ActionScript Code:

[LEFT]import flash.external.ExternalInterface; 
function GetUserIdFromSite() 
{     
textBoxUserIdFromSite.text = ExternalInterface.call("getUserId"); 
}
[/LEFT]

JavaScript
Code:

 
function getUserId()
{ 
var userID = "foo"; return userID; 
}

I have set <param name=“allowScriptAccess” value=“always” />

All i get in the textbox is null. Whats wrong?