绑定DataGridView时出现值无效错误

[gunziyang]

代码和报错如下，改写自msdn里的例子，我想让Title这个ComboxColumn显示的是King或Sir的文字，然后值是0或1。

问题1：为什么会出现这个错误，该如何修改？
问题2：有时候（不是在这个代码中出现的问题）在某个单元格下拉列表选择了King之后，当焦点离开这个单元格之后，该单元格会变成value的数字形式，即选了King，鼠标离开单元格后，单元格会变成0，这是为什么，该如何修改？

小弟分不多，还请大家多多包涵，先谢谢了！

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace TestDataGridViewComboBoxColumn
{
    public partial class Form1 : Form
    {
        BindingSource bindingSource1 = new BindingSource();
        DataGridView dataGridView1 = new DataGridView();
        
        
        public enum Title
        {
            King,
            Sir
        }
        
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            EnumsAndComboBox_Load(null, null);
        }

        private void EnumsAndComboBox_Load(object sender, System.EventArgs e)
        {
            // Populate the data source.
            
            bindingSource1.Add(new Knight(Title.King));
            bindingSource1.Add(new Knight(Title.King));
            bindingSource1.Add(new Knight(Title.Sir));
            bindingSource1.Add(new Knight(Title.Sir));
            bindingSource1.Add(new Knight(Title.Sir));

            // Initialize the DataGridView.
            dataGridView1.AutoGenerateColumns = false;
            dataGridView1.AutoSize = true;
            dataGridView1.DataSource = bindingSource1;

            dataGridView1.Columns.Add(CreateComboBoxWithEnums());



            // Initialize the form.
            this.Controls.Add(dataGridView1);
            this.AutoSize = true;
            this.Text = "DataGridView object binding demo";
        }

        DataGridViewComboBoxColumn CreateComboBoxWithEnums()
        {
            DataGridViewComboBoxColumn combo = new DataGridViewComboBoxColumn();

            combo.ValueType = typeof(Title);
            combo.DataSource = new Title[]{Title.King, Title.Sir}
.Select(element => new {display = element.ToString(), value = Convert.ToInt32(element) })
.ToList();
            combo.DisplayMember = "display";
            combo.ValueMember = "value";
            combo.DataPropertyName = "Title";
            combo.Name = "Title";
            return combo;
        }
        #region "business object"
        private class Knight
        {

            private Title hisTitle;

            public Knight(Title title)
            {
                hisTitle = title;
                
            }

            public Knight()
            {
                hisTitle = Title.Sir;
              
            }

            
            public Title Title
            {
                get
                {
                    return hisTitle;
                }
                set
                {
                    hisTitle = value;
                }
            }
        }
        #endregion
    }
}

[gunziyang]

自己顶一个，请大家帮帮忙啊