[jQuery] help please. ajax call get status 0 and responseText null

[jQuery] help please. ajax call get status 0 and responseText null


here is source code. In my javascript function I use jquery to make a
ajax call. myurl is a jsp in localhost which will output a xml.
However i got status 0(not 200). What happen?
$.ajax({
    type:"POST",
    url:myurl,
    data: params,
    complete:function(XMLHttpRequest,textStatus){
        alert("respons status "+XMLHttpRequest.status+" content:
"+XMLHttpRequest.responseText+" header:
"+XMLHttpRequest.getAllResponseHeaders());
    }
    });
Here is the jsp:
<%response.setContentType("text/xml");
response.setHeader("Cache-Control", "no-cache");
response.setHeader("Pragma", "no-cache");
String ajaxRs="<?xml version=\"1.0\" encoding=\"ISO-8859-1\"?>";
ajaxRs=ajaxRs+"<response>";
ajaxRs=ajaxRs+"<message>test!</message>";
ajaxRs=ajaxRs+"</response>";
        System.out.println(ajaxRs);
        response.getWriter().write(ajaxRs);
%>
backend is websphere+ db2.
Can anybody help me?
Thanks a lots!