GridView指定的参数已超出有效值的范围

GridView在更新过程中
异常详细信息: System.ArgumentOutOfRangeException: 指定的参数已超出有效值的范围。
参数名: index
本段代码如下protected void GridView1_RowUpdating(object sender, GridViewUpdateEventArgs e)
    {
        
        string stuID = GridView1.DataKeys[e.RowIndex].Value.ToString();
        
        TextBox tb1 = (TextBox)GridView1.Rows[e.RowIndex].Cells[2].Controls[0];
        string g1 = tb1.Text;// 显示错误在这两行上        string g2 = ((TextBox)GridView1.Rows[e.RowIndex].Cells[3].Controls[0]).Text;
        string g3 = ((TextBox)GridView1.Rows[e.RowIndex].Cells[4].Controls[0]).Text;
        string g4 = ((TextBox)GridView1.Rows[e.RowIndex].Cells[5].Controls[0]).Text;
        string updateSql = String.Format("update studentInfo set grade1='{0}',grade2='{1}',grade3='{2}',grade4='{3}' where stuID='{4}'",g1,g2,g3,g4,stuID);        SqlConnection conn = new SqlConnection("server=.;database=Elect;Integrated Security=SSPI");
        conn.Open();
        SqlCommand cmd = new SqlCommand(updateSql, conn);
        int count=cmd.ExecuteNonQuery();
        conn.Close();
        if (count > 0)
        {
            Response.Write("<script>alert('更新成功！')</script>");
        }
        GridView1.EditIndex = -1;
        BindGrid();
    }另：GridView总共是7列13排