Firstly, I would kick the Ranch Office that they should by default disable HTML in messages. I tried that before with vain. Also parsing of the HTML entities is troublesome since some time (check the quote/edit screens). I don't have the motivation anymore to report forum related bugs/issues myself.
Regarding to your problem: in the future please use the Struts forum for Struts related questions. All what I can tell is that the bean with the managed bean name "username" isn't been placed in any of the scopes.