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！";            }        }