C# 请问造成这种现象的原因是什么？

如图：无法移到下一条记录，但是却可以移到最后一条记录,哪位大神解答一下，鄙人在此谢过。

代码如下：

{
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using ClassDB;
namespace HPCIMTS_admin
public partial class frmPatienttracking : Form
{
DataSet vw_病人查询;
public frmPatienttracking()
{
InitializeComponent();
}

    private void frmPatienttracking_Load(object sender, EventArgs e)
    {
        ClassDB.ClassDB db = new ClassDB.ClassDB();
        string strSql = "select*from vw_病人查询";
        vw_病人查询 = db.getDataSet(strSql);
        bindingSource1.DataSource = vw_病人查询.Tables[0];
        bindingNavigator1.BindingSource = bindingSource1;
        txt_Pno.DataBindings.Add("Text",bindingSource1,"病案号");
    }

    private void bindingNavigatorMovePreviousItem_Click(object sender, EventArgs e)
    {
        bindingSource1.MovePrevious();
    }

    private void bindingNavigatorMoveNextItem_Click(object sender, EventArgs e)
    {
        bindingSource1.MoveFirst();
    }

    private void bindingNavigatorMoveFirstItem_Click(object sender, EventArgs e)
    {
        bindingSource1.MoveFirst();
    }

    private void bindingNavigatorMoveLastItem_Click(object sender, EventArgs e)
    {
        bindingSource1.MoveLast();
    }
    }
    }

自己已经把问题解决，不过还是要谢谢回答我问题的人。

没有代码，天知道~~~