ritestato il mio codice e funziona

codice:
public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            DataTable dt = new DataTable();
            for (int n = 0; n < 2; n++)
                dt.Columns.Add(new DataColumn("col" + n.ToString(), typeof(System.Int16)));

            for (int n = 0; n < 10; n++)
                dt.Rows.Add(n, n * 10);

            this.dataGridView1.DataSource = dt;
            this.dataGridView1.SelectionMode = DataGridViewSelectionMode.FullRowSelect;
        }

        private void button1_Click(object sender, EventArgs e)
        {
            int index = this.dataGridView1.CurrentRow.Index;
            if (index == this.dataGridView1.RowCount - 1)
                return;
            this.dataGridView1.CurrentCell = this.dataGridView1.Rows[index + 1].Cells[0];
        }

        private void button2_Click(object sender, EventArgs e)
        {
            int index = this.dataGridView1.CurrentRow.Index;
            if (index == 0)
                return;
            this.dataGridView1.CurrentCell = this.dataGridView1.Rows[index - 1].Cells[0];
        }

    }