ASP.NET，未知的身份验证机制

在win7 64位系统下开发的网站，要集成AD域认证，在开发环境一切正常，部署到server2003上，iis设置集成windows认证，运行时总是报错“未知的身份验证机制”。
主要涉及到两个文件，LoginPage.cs负责获取域用户名，首先判断在数据库中是否存在匹配的记录，如果有则获取用户信息后正常访问，如果没有则调用AdHelper.cs中的GetUserValue方法去AD域中查询，把查询的结果写入数据库，然后正常访问。
LoginPage.cs
        public string ULogin()
        {
            string errorMsg;
            
            string username;            username = Page.User.Identity.Name;            if (Session["IsLogin"] == null)
            {
                UserSystem userSystem = new UserSystem();
                User userInfor = new User();
                userInfor = userSystem.Get_SintUser(username);                if (userInfor == null)
                {
                    AdHelper adHelper = new AdHelper();
                    User userAD = new User();
                    userAD = adHelper.GetUserValue(username);                    if (userAD != null)
                    {
                        userAD.FUserName = username;
                        userAD.FStatus = 1;
                        userAD.FIsAdmin = 0;
                        userAD.FCreateTime = DateTime.Now;                    }
                }
            }
        }
AdHelper.cs
        public string adPath = ConfigurationManager.AppSettings["LDAP"].ToString();
        public string adUserName = ConfigurationManager.AppSettings["adUserName"].ToString();
        public string adUserPassword = ConfigurationManager.AppSettings["adUserPassword"].ToString();
        /// <summary>
        /// 根据用户名获取用户信息
          /// </summary>
        /// <param name="username">用户名</param>
        /// <returns>User</returns>
        public User GetUserValue(string username)
        {
            DirectoryEntry entry = new DirectoryEntry(adPath, adUserName, adUserPassword);
            User user = new User();
            try
            {
                object obj = entry.NativeObject;
                DirectorySearcher search = new DirectorySearcher(entry);
                search.Filter = "(SAMAccountName=" + username + ")";
                search.PropertiesToLoad.Add("Employeeid");
                search.PropertiesToLoad.Add("displayname");
                
                SearchResult result = search.FindOne();
                if (null == result)
                {
                    return null;
                }
                user.FUserNumber = result.Properties["Employeeid"][0].ToString();
                user.FUserFullName = result.Properties["displayname"][0].ToString();
            }
            catch (Exception ex)
            {
                throw new Exception("Error authenticating user. " + ex.Message);
            }
            entry.Close();
            
            return user;
        }请各位大侠帮忙解决！！asp.netAD域