how to manage user session?

Question

dear all I have a webservice which contains 2 methods: [WebMethod(EnableSession=true)] public void Login(string usercode, string password) { Session["usercode"] = usercode; Session["password"] = password; } [WebMethod(EnableSession=true)] public string CheckUserInfo() { return Session["usercode"] ; } Why does method CheckUserInfo() return NULL? FYI: I call Login() firstly from Windows App, CheckUserInfo() only aims to get info of user who logined already. Thank you too much, Best Regards, Khanh