добавить данные в бд из 4 textbox по нажатию кнопки

ERROR: validation failed for one or more entities. See "EntityValidationErrors" property for more details.

 public PageAddTest()
        {
            InitializeComponent();
            cmbxQuestion.SelectedValuePath = "id_question";
            cmbxQuestion.DisplayMemberPath = "nameQuestion";
            cmbxQuestion.ItemsSource = AppConnect.modelOdb.Question.ToList();

        }

        private void BtnSubmit_Click(object sender, RoutedEventArgs e)
        {
            if (Rbtn1.IsChecked == false &&
                Rbtn2.IsChecked == false &&
                Rbtn3.IsChecked == false &&
                Rbtn4.IsChecked == false 
                )
            {
                MessageBox.Show("error", "error",
                    MessageBoxButton.OK, MessageBoxImage.Information);
                return;
            }
            try
            {
                Answers userObj = new Answers()
                {
                    Question = cmbxQuestion.SelectedItem as Question,
                    isCorrect = false,

                };

                AppConnect.modelOdb.Answers.Add(new Answers() { nameAnswer = TxbAnswer1.Text });
                AppConnect.modelOdb.Answers.Add(new Answers() { nameAnswer = TxbAnswer2.Text });
                AppConnect.modelOdb.Answers.Add(new Answers() { nameAnswer = TxbAnswer3.Text });
                AppConnect.modelOdb.Answers.Add(new Answers() { nameAnswer = TxbAnswer4.Text });
                AppConnect.modelOdb.Answers.Add(userObj);
                AppConnect.modelOdb.SaveChanges();

                MessageBox.Show("Данные добавлены", "",
                MessageBoxButton.OK, MessageBoxImage.Exclamation);



            }
            catch (Exception ex)
            {
                MessageBox.Show("Ошибка добавления данных " + ex.Message, "",
                   MessageBoxButton.OK, MessageBoxImage.Error);
            }
        }