Webservice Session有关问题

[WebMethod(Description = "Hello Demo", EnableSession = true)]
        public string HelloWorld()
        {
            if (System.Web.HttpContext.Current.Session.Count == 0)
            {
                return "Hello,World";
            }
            else
            {
                return "Hello World, " + System.Web.HttpContext.Current.Session["UserName"].ToString();
            }
        }

[WebMethod(Description = "登录", EnableSession = true)]
        public string ClientLogin(string uName, string pwd)
        {
            //判断帐号是否正确
            。。。
                //创建一个session
                System.Web.HttpContext.Current.Session["UserName"] = uName;
                MySQLHelp.SetSession("Login", 0);
                // return "Hello, " + System.Web.HttpContext.Current.Session["UserName"].ToString();
                return "OK:" + ds.Tables[0].Rows[0]["Cname"].ToString();
            }
            else
            {
                return "error: 密码不正确，注意区分大小写！";
            }
        }