void VerifyUsername(object o)
        {
            if (o != null)
            {
                string username = o.ToString();

                bool available = UserManagement.CheckUsernameAvailability(username);

                Dispatcher.BeginInvoke(new Action <bool>(VerifyUsername_Finished), System.Windows.Threading.DispatcherPriority.Background, new object[] { available });
            }
        }