jquery 在struts2项目中的问题

 页面中的jquery调用   $.ajax({
                              type : "POST",
                              url  : "MBlogin.action",
                              data : "username="+username+"&&pw="+pw,
                              error : function(){
                                alert("error");)
                              },
                              success : function (msg){
                                if(msg==""){
                                    return false;
                                 }
                                 else{
                                    alert(msg););)
                                 }
                              }
                        });
action中相关代码：
                  HttpServletResponse resp = GetContext.getHttpServletResponse();
                  resp.setCharacterEncoding("UTF-8".);
                  PrintWriter out = resp.getWriter();
                  String msg = "调用成功";
                  out.print(msg);
                  return  null;

问题：在tomcat下执行完全正常，但在was下运行时可以调用到action方法，但返回页面时会执行error：function，如代码会alert出error，请高手解答是哪里出了问题？