I'm begining with Struts 2, but I'm having the same problem when trying to do AJAX client side validation.
I added <sx:head /> and <sx:submit validate="true" /> in order to do this.
But just Chengwei Lee, the first time I click on submit it shows the error message, but when I click it again it shows the new error message without clearing the last one.
I've searched on the web but haven't found the solution. Hope you can help me. Thanks in advance.