Не сериализуется лист в C#

Получен xml:

    <?xml version="1.0"?>
<ArrayOfIndividualNum xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <IndividualNum />
</ArrayOfIndividualNum>

Код главного класса:

    using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace kursach
{
    [Serializable]
    public class Investor
    {
        protected string name;
        protected string gender;
        protected string address;
        protected string birthday;
        public void setName(string yourName) { name = yourName; }
        public void setGender(string yourGender) { gender = yourGender; }
        public void setAddress(string yourAddress) { address = yourAddress; }
        public void setBirthday(string yourBirthday) { birthday = yourBirthday; }
        public string putName() { return name; }
        public string putGender() { return gender; }
        public string putAddress() { return address; }
        public string putBirthday() { return birthday; }
        // Конструктор без параметров
        public Investor()
        {
            name = "";
            gender = "";
            address = "";
            birthday = "";
        }
        public Investor(string one)
        {
            name = "one";
            gender = "";
            address = "";
            birthday = "";
        }
    }
}

Код наследника:

    using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.IO;
namespace kursach
{
    [Serializable]
    public class IndividualNum : Investor
    {   
        private int numInvest;
        private int start;
        private string date;
        public void setNumInvest(int yourInvest) { numInvest = yourInvest; }
        public void setStart(int yourStart) { start = yourStart; }
        public void setDate(string yourDate) { date = yourDate; }
        public int getNumInvest() { return numInvest; }
        public int getStart() { return start; }
        public string getDate() { return date; }
        // Конструктор без параметров.
        public IndividualNum() : base()
        {
            numInvest = 0;
            start = 0;
            date = "";
        }
        public IndividualNum(string one) : base(one)
        {
            numInvest = 16;
            start = 13;
            date = "";
        }
    }
}

Ну и код самой формы:

    using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Collections.Generic;
using System.IO;
using System.Xml.Serialization;
using System.Runtime.Serialization;
namespace kursach
{
    public partial class Form1 : Form
    {
        public List<IndividualNum> allPeople = new List<IndividualNum>(); // Все люди из расписания.
        private string nameOpenFile;
        // Изначальная видимость кнопок.
        public void BtnFalse()
        {
            if (dataGridView1.RowCount == 0)
            {
                this.Save.Enabled = false;
                this.редактироватьТабилцуToolStripMenuItem.Enabled = false;
                this.удалитьВыделеннуюСтрокуToolStripMenuItem.Enabled = false;
                this.очиститьТаблицуToolStripMenuItem.Enabled = false;
                this.SaveHow.Enabled = false;
                this.RedactButton.Enabled = false;
                allPeople.Clear();
            }
            if (this.RequestDataGridView.RowCount == 0)
            {
                this.выполнитьЗапросToolStripMenuItem.Enabled = false;
                this.сохранитьЗапросToolStripMenuItem.Enabled = false;
                this.удалитьЗапросToolStripMenuItem.Enabled = false;
            }
            nameOpenFile = "";
        }
        // Включение кнопок если таблица не пуста.
        public void BtnTrue()
        {
            if (this.dataGridView1.RowCount != 0)
            {
                if (nameOpenFile != "")
                    this.Save.Enabled = true;
                this.SaveHow.Enabled = true;
                this.выполнитьЗапросToolStripMenuItem.Enabled = true;
                this.редактироватьТабилцуToolStripMenuItem.Enabled = true;
                this.удалитьВыделеннуюСтрокуToolStripMenuItem.Enabled = true;
                this.очиститьТаблицуToolStripMenuItem.Enabled = true;
                this.RedactButton.Enabled = true;
            }
            if (this.RequestDataGridView.RowCount != 0)
            {
                this.выполнитьЗапросToolStripMenuItem.Enabled = true;
                this.сохранитьЗапросToolStripMenuItem.Enabled = true;
                this.удалитьЗапросToolStripMenuItem.Enabled = true;
            }
        }
        // Заполнение таблицы (метод - 0 (добавление новой), 1 - изменение имеющейся, любой другой - добавление).
        public void AddRow(IndividualNum human, int method)
        {
            int rowCount = 0;
            switch (method)
            {
                case 0:
                    this.dataGridView1.Rows.Add();
                    rowCount = this.dataGridView1.Rows.Count - 1;
                    break;
                case 1:
                    rowCount = this.dataGridView1.CurrentRow.Index;
                    break;
                default:
                    this.dataGridView1.Rows.Add();
                    rowCount = this.dataGridView1.Rows.Count - 1;
                    break;
            }
            int cells = 0;
            this.dataGridView1.Rows[rowCount].Cells[cells++].Value = human.putName();
            this.dataGridView1.Rows[rowCount].Cells[cells++].Value = human.putGender();
            this.dataGridView1.Rows[rowCount].Cells[cells++].Value = human.putAddress();
            this.dataGridView1.Rows[rowCount].Cells[cells++].Value = human.putBirthday();
            this.dataGridView1.Rows[rowCount].Cells[cells++].Value = human.getNumInvest();
            this.dataGridView1.Rows[rowCount].Cells[cells++].Value = human.getDate();
            this.dataGridView1.Rows[rowCount].Cells[cells++].Value = human.getStart();
        }
        // Конструктор формы.
        public Form1()
        {
            InitializeComponent();
            BtnFalse();
        }
        // Выход.
        private void exit_Click(object sender, EventArgs e)
        {
            //if (this.dataGridView1.RowCount == 1)
                this.Close();
           // else
           // {
                // Сообщение о том что может сохранить?
           // }
        }
        // Добавление данных вкладчика.
        private void добавитьВкладчикаToolStripMenuItem_Click(object sender, EventArgs e)
        {
            input newInvest = new input(1);
            newInvest.RequestMethod = false;
            newInvest.ShowDialog();
            if (newInvest.DontClose)
            {
                AddRow(newInvest.Invest, 0);
                allPeople.Add(newInvest.Invest);
                BtnTrue();
            }
        }
        // Удаление выделенной строки.
        private void удалитьВыделеннуюСтрокуToolStripMenuItem_Click(object sender, EventArgs e)
        {
            if (this.dataGridView1.CurrentCellAddress.X != -1)
            {
                this.dataGridView1.CurrentRow.Selected = true;
                DialogResult res = MessageBox.Show("Удалить выделенную строку?\nэто путь в один конец", "Не торопись подумой", MessageBoxButtons.YesNo);
                if (res == DialogResult.Yes)
                {
                    this.dataGridView1.Rows.Remove(this.dataGridView1.CurrentRow);
                    if (this.dataGridView1.RowCount == 0)
                        BtnFalse();
                    else
                        BtnTrue();
                }
            }
        }
        // Редактироание выделенной строки.
        private void редактироватьТабилцуToolStripMenuItem_Click(object sender, EventArgs e)
        {
            if (this.dataGridView1.CurrentCellAddress.X != -1)
            {
                this.dataGridView1.CurrentRow.Selected = true;
                int count = 0;
                foreach (IndividualNum human in allPeople)
                    if (count == this.dataGridView1.CurrentRow.Index)
                    {
                        input edit = new input(human);
                        edit.RequestMethod = false;
                        edit.ShowDialog();
                        if (edit.DontClose)
                        {
                            AddRow(human, 1);
                            allPeople[count] = edit.Invest;
                            this.dataGridView1.CurrentRow.Selected = true;
                        }
                        break;
                    }
                    else
                        count++;
            }
        }
        private void очиститьТаблицуToolStripMenuItem_Click(object sender, EventArgs e)
        {
            DialogResult res = MessageBox.Show("Серъёзно? прям всю отчистить?", "Может не надо?", MessageBoxButtons.YesNo);
            if (res == DialogResult.Yes)
            {
                this.dataGridView1.Rows.Clear();
                BtnFalse();
            }
        }
        private void Open_Click(object sender, EventArgs e)
        {
            if (openFileDialog1.ShowDialog() == DialogResult.OK)
            {
                dataGridView1.Rows.Clear();
                BtnFalse();
                //StreamReader streamReader = new StreamReader(openFileDialog1.FileName);
                //nameOpenFile = openFileDialog1.FileName;
                //string investors = streamReader.ReadToEnd();
                //streamReader.Close();
                nameOpenFile = openFileDialog1.FileName;
                XmlSerializer serializ = new XmlSerializer(typeof(List<IndividualNum>));
                FileStream file = new FileStream(nameOpenFile, FileMode.Open, FileAccess.Read);
                allPeople = (List<IndividualNum>)serializ.Deserialize(file);
                file.Close();
                //string[] splitInvestors = investors.Split(new char[] {';', 't'});
                //int rowCount = 0, cellsCount = 0;
                //this.dataGridView1.Rows.Add();
                //foreach (string str in splitInvestors) {
                //    this.dataGridView1.Rows[rowCount].Cells[cellsCount++].Value = str;
                //    if (cellsCount == 6)
                //    {
                //        rowCount++;
                //        this.dataGridView1.Rows.Add();
                //        cellsCount = 0;
                //    }
                //}
                //if (this.dataGridView1.RowCount != 0)
                //{
                //    BtnTrue();
                //    this.Save.Enabled = true;
                //}
            }
        }
        private void Save_Click(object sender, EventArgs e)
        {
            if (nameOpenFile != "")
            {
                XmlSerializer serializ = new XmlSerializer(typeof(List<IndividualNum>));
                FileStream file = new FileStream(nameOpenFile, FileMode.Open, FileAccess.Write);
                serializ.Serialize(file, allPeople);
                file.Close();
            }
        }
        private void SaveHow_Click(object sender, EventArgs e)
        {
            if (saveFileDialog1.ShowDialog() == DialogResult.OK)
            {
                nameOpenFile = saveFileDialog1.FileName;
            //    if (nameOpenFile != "")
            //    {
                    //IndividualNum test = new IndividualNum();
                    //allPeople.Add(test);
                    //int count = 0;
                    //foreach (IndividualNum human in allPeople)
                    //    if (human.putName() == "1")
                    //        count++;
                    //XmlSerializer serializ = new XmlSerializer(typeof(List<IndividualNum>));
                    //FileStream file = new FileStream(nameOpenFile, FileMode.Create, FileAccess.Write, FileShare.None);
                    //serializ.Serialize(file, allPeople);
                    //file.Close();
                    //XmlSerializer ser = new XmlSerializer(typeof(List<String[]>));
                    //StreamWriter sw = new StreamWriter(@"D:\2.xml");
                    //ser.Serialize(sw, allPeople);
                    //sw.Close();

            //XmlSerializer ser = new XmlSerializer(typeof(IndividualNum));

            //TextWriter writer = new StreamWriter(nameOpenFile);
            //ser.Serialize(writer, allPeople);
            //writer.Close();
                allPeople.Clear();
                IndividualNum test = new IndividualNum("his");
                allPeople.Add(test);
                using (FileStream fs = new FileStream(nameOpenFile, FileMode.Create, FileAccess.Write))
                {
                    XmlSerializer serializer = new XmlSerializer(allPeople.GetType());
                    serializer.Serialize(fs, allPeople);
                }
                    //XmlSerializer xml = new XmlSerializer(typeof(IndividualNum));
                    //StringWriter strWriter = new StringWriter();
                    //xml.Serialize(strWriter, allPeople);
                //}
                //XmlTextWriter xw = new XmlTextWriter(nameOpenFile, Encoding.UTF8);
                //xw.Formatting = Formatting.Indented;
                //XmlDictionaryWriter writer = XmlDictionaryWriter.CreateDictionaryWriter(xw);
                //DataContractSerializer ser = new DataContractSerializer(typeof(IndividualNum));
                //ser.WriteObject(writer, allPeople);
                //writer.Close();
                //xw.Close();
            }
        }
    }
}

И код где я пытаюсь сериализовать:

if (saveFileDialog1.ShowDialog() == DialogResult.OK)
        {
            nameOpenFile = saveFileDialog1.FileName;
        //    if (nameOpenFile != "")
        //    {
                //IndividualNum test = new IndividualNum();
                //allPeople.Add(test);
                //int count = 0;
                //foreach (IndividualNum human in allPeople)
                //    if (human.putName() == "1")
                //        count++;
                //XmlSerializer serializ = new XmlSerializer(typeof(List<IndividualNum>));
                //FileStream file = new FileStream(nameOpenFile, FileMode.Create, FileAccess.Write, FileShare.None);
                //serializ.Serialize(file, allPeople);
                //file.Close();
                //XmlSerializer ser = new XmlSerializer(typeof(List<String[]>));
                //StreamWriter sw = new StreamWriter(@"D:\2.xml");
                //ser.Serialize(sw, allPeople);
                //sw.Close();

        //XmlSerializer ser = new XmlSerializer(typeof(IndividualNum));

        //TextWriter writer = new StreamWriter(nameOpenFile);
        //ser.Serialize(writer, allPeople);
        //writer.Close();
            allPeople.Clear();
            IndividualNum test = new IndividualNum("his");
            allPeople.Add(test);
            using (FileStream fs = new FileStream(nameOpenFile, FileMode.Create, FileAccess.Write))
            {
                XmlSerializer serializer = new XmlSerializer(allPeople.GetType());
                serializer.Serialize(fs, allPeople);
            }
                //XmlSerializer xml = new XmlSerializer(typeof(IndividualNum));
                //StringWriter strWriter = new StringWriter();
                //xml.Serialize(strWriter, allPeople);
            //}
            //XmlTextWriter xw = new XmlTextWriter(nameOpenFile, Encoding.UTF8);
            //xw.Formatting = Formatting.Indented;
            //XmlDictionaryWriter writer = XmlDictionaryWriter.CreateDictionaryWriter(xw);
            //DataContractSerializer ser = new DataContractSerializer(typeof(IndividualNum));
            //ser.WriteObject(writer, allPeople);
            //writer.Close();
            //xw.Close();