使用datagridView时，INSERT命令会发生异常，而删除和更新在使用Access数据库的C＃中可以正常工作

使用我表单中的保存按钮，除INSERT命令外，所有操作（更新，删除）均正常运行。帮帮我...

public partial class frmeditaccess : Form
{
    string table = "master";

    OleDbDataAdapter da;
    OleDbCommandBuilder cb;
    DataTable dt;
    OleDbConnection conn;
    string query;

    public frmeditaccess()
    {
        InitializeComponent();
    }

    private void btload_Click(object sender, EventArgs e)
    {
        try
        {
            conn = new OleDbConnection();
            conn.ConnectionString = @"Provider=Microsoft.Jet.OLEDB.4.0;" + @"Data source= C:\Users\ViPuL\Documents\Visual Studio 2010\Projects\feedback@MERI\feedback@MERI\bin\feedback.mdb";
            query = string.Format("SELECT * FROM {0}", table);
            da = new OleDbDataAdapter(query, conn);
            dt = new DataTable();
            dataGridView1.DataSource = dt;
        }
        catch (Exception ex)
        {
            MessageBox.Show("Failed due to " + ex.Message);
        }
    }

    private void btsave_Click(object sender, EventArgs e)
    {
        try
        {
            cb = new OleDbCommandBuilder(da);
            da.Update(dt);      //here update, delete are working. Only, Insert throws exception of syntax error in INSERT command.
        }
        catch (Exception ex)
        {
            MessageBox.Show("Failed due to " + ex.Message);
        }
    }