var loginResult = mgr.Login((ILoginCredential)cred);                var isLoggedIn = mgr.IsLoggedIn;

as false, when the login fails. So that one can test in the Client, and not have an exception.

//Client
        void DoIt()        {            NorthwindManager mgr = new NorthwindManager();             //IdeaBlade.Core.IdeaBladeConfig.ConfigFileAssembly = Assembly.GetExecutingAssembly();            var configInstance = IdeaBlade.Core.IdeaBladeConfig.Instance;            configInstance.ObjectServer.ClientSettings.IsDistributed = false;            configInstance.ObjectServer.ServerSettings.AllowAnonymousLogin = false;            configInstance.ObjectServer.ServerSettings.LoginManagerRequired = true;            configInstance.Logging.ShouldLogSqlQueries = true;            configInstance.Logging.LogFile = "MyLogFile.xml"; //not working.             Console.WriteLine("Thread principal before login: {0}", System.Threading.Thread.CurrentPrincipal.Identity.Name);            bool isLoggedIn = false;            bool loginResult = false;            try            {                // Login will null credentials.  The LoginManager will decide what to do ...                LoginCredential cred = new LoginCredential("john", "password", "domain");                //loginResult = mgr.Login((ILoginCredential)null);                 loginResult = mgr.Login((ILoginCredential)cred);                isLoggedIn = mgr.IsLoggedIn;                Console.WriteLine("Thread principal after login: {0}", System.Threading.Thread.CurrentPrincipal.Identity.Name);            }            catch (LoginException le)            {                Console.WriteLine("LoginException: " + le.Message);                isLoggedIn = mgr.IsLoggedIn;                Console.WriteLine("Press ENTER to exit...");                Console.ReadLine();                return;            }            catch (EntityServerException ese)            {                Console.WriteLine("EntityServerException Login failed: " + ese.Message);                isLoggedIn = mgr.IsLoggedIn;                Console.WriteLine("Press ENTER to exit...");                Console.ReadLine();                return;            }            catch (Exception ex)            {                bool isLogged = mgr.IsLoggedIn;                Console.WriteLine(ex.Message);                return;            }

            // etc....
         }

//Server
        public IPrincipal Login(ILoginCredential credential, EntityManager entityManager)        {            if (credential == null)            {                // if running n-tier the user's Windows credentials will be passed and available on the thread:                var principal = System.Threading.Thread.CurrentPrincipal;                if (principal.Identity.IsAuthenticated)                {                    Logger.WriteMsg(string.Format("principal is {0}", principal.Identity.Name));                    // Note that we can't return the WindowsPrincipal/WindowsIdentity back to the client, so                    // create a new one, here we use the DevForce UserBase class, but you can create your own too.                     return CreateUser(principal);                }                else                {                    // This is here for 2-tier testing, since you'll probably want to throw an error or do                    // some custom logic in n-tier.  When not running n-tier, the thread principal has not been set                     // but you can obtain the Windows Identity and use that.                    var wi = WindowsIdentity.GetCurrent();                    Logger.WriteMsg(string.Format("wi is {0}", wi.Name));                    WindowsPrincipal wp = new WindowsPrincipal(wi);                    return CreateUser(wp);                }            }            else            {                Logger.WriteMsg("Non-Windows Login");                GenericIdentity gi = null;                if (credential.UserName.Equals("john")) //change to somthing else to force failure                {                    gi = new GenericIdentity(credential.UserName, "MyAuthoType");                }                else                {
                    //This is the way of getting IsAuthenticated set to false                    gi = new GenericIdentity("", "MyAuthoType");                     //This will throw in EntityServer                    // throw new LoginException(LoginExceptionType.InvalidUserName, credential.Domain, credential.UserName);                }                GenericPrincipal gp = new GenericPrincipal(gi, null);                Logger.WriteMsg("Non-Windows Login Completed.");                return CreateUser(gp);            }            throw new NotImplementedException("Some Login Error");        }         private UserBase CreateUser(IPrincipal currentUser)        {            // The UserBase and UserIdentity classes are custom IPrincipal/IIdentity implementations            // within DevForce.               UserIdentity identity = new UserIdentity(currentUser.Identity.Name, currentUser.Identity.AuthenticationType, currentUser.Identity.IsAuthenticated);            bool isInRole = currentUser.IsInRole("");            var isAuth = currentUser.Identity.IsAuthenticated;             // You can determine what roles to set, if any.            string[] roles = new string[] { };             if (isAuth)            {                Logger.WriteMsg("UserBase created.");                return new UserBase(identity, roles);            }            //Will result in an EntityServerException in the Client            Logger.WriteMsg("Null UserBase returned.");            return null;        }

thanks
John