This is the login function (after I validate user name and password, I load user data into "user" variable and call Login function:

public static void Login(IUser user)
{
    HttpResponse Response = HttpContext.Current.Response;
    HttpRequest Request = HttpContext.Current.Request;

    FormsAuthenticationTicket ticket = new FormsAuthenticationTicket(1,
        user.UserId.ToString(), DateTime.Now, DateTime.Now.AddHours(12), false,
        UserResolver.Serialize(user));

    HttpCookie cookie = new HttpCookie(FormsAuthentication.FormsCookieName,
        FormsAuthentication.Encrypt(ticket));
    cookie.Path = FormsAuthentication.FormsCookiePath;

    Response.Cookies.Add(cookie);

    string redirectUrl = user.HomePage;

    Response.Redirect(redirectUrl, true);
}

UserResolver is the following class:

public class UserResolver
{
    public static IUser Current
    {
        get
        {
            IUser user = null;
            if (HttpContext.Current.User.Identity.IsAuthenticated)
            {
                FormsIdentity id = (FormsIdentity)HttpContext.Current.User.Identity;
                FormsAuthenticationTicket ticket = id.Ticket;
                user = Desrialize(ticket.UserData);
            }
            return user;
        }
    }

    public static string Serialize(IUser user)
    {
        StringBuilder data = new StringBuilder();
        StringWriter w = new StringWriter(data);
        string type = user.GetType().ToString();
        //w.Write(type.Length);
        w.WriteLine(user.GetType().ToString());
        StringBuilder userData = new StringBuilder();
        XmlSerializer serializer = new XmlSerializer(user.GetType());
        serializer.Serialize(new StringWriter(userData), user);
        w.Write(userData.ToString());
        w.Close();
        return data.ToString();
    }

    public static IUser Desrialize(string data)
    {
        StringReader r = new StringReader(data);
        string typeStr = r.ReadLine();
        Type type=Type.GetType(typeStr);
        string userData = r.ReadToEnd();
        XmlSerializer serializer = new XmlSerializer(type);
        return (IUser)serializer.Deserialize(new StringReader(userData));
    }
}

And the global.asax implements the following:

void Application_PostAuthenticateRequest(Object sender, EventArgs e)
{
    IPrincipal p = HttpContext.Current.User;
    if (p.Identity.IsAuthenticated)
    {
        IUser user = UserResolver.Current;
        Role[] roles = user.GetUserRoles();
        HttpContext.Current.User = Thread.CurrentPrincipal =
            new GenericPrincipal(p.Identity, Role.ToString(roles));
    }
}

First question: Am I do it right?

Second question - weird thing! The user variable I pass to Login has 4 members: UserName, Password, Name, Id. When UserResolver.Current executed, I got the user instance. I descided to change the user structure - I add an array of Warehouse object. Since that time, when UserResolver.Current executed (after Login), HttpContext.Current.User.Identity.IsAuthenticated was false and I couldn't get the user data. When I removed the Warehouse[] from user structure, it starts to be ok again and HttpContext.Current.User.Identity.IsAuthenticated become true after I Login.

What is the reason to this weird behaviour?