如何修复错误System.Data.Entity.Infrastructure.DbUpdateException？

Question

没有记录添加到表中。这些记录不是重复的，也不是pk类型

private void btn_ok_Click(object sender, RoutedEventArgs e)
{
    Customer c = new Customer();
    c.CustomerName = txt_customername.Text.Trim();
    c.CustomerTel = txt_telcustomer.Text.Trim();
    c.CustomerAddress = txt_customeraddress.Text.Trim();
    c.StartDate = lbl_Data.Content.ToString();
    c.UserID = publicvariable.guserId;

    database.Customers.Add(c);
    database.SaveChanges();
    MessageBox.Show("مشتری جدید با موفقیت ثبت شد");
}