Grid view in windows form c#

Question

I am having a grid view when i double click on the row its  value  should display in the text box and combobox respectively   but m getting error and its not displaying ...
Pls  help me  ...
Here s my code

        private void dataGridView1_DoubleClick(object sender, EventArgs e)
          {

            try

            {

                DataTable dt = new DataTable();

                OleDbDataAdapter da = new OleDbDataAdapter("select class_standard,subjectcode,subjectname from tblsubject where subjectcode=" +

             Convert.ToInt16(dataGridView1.SelectedRows[0].Cells[0].Value.ToString()) + " ", con);

                da.Fill(dt);

                //display now the record in the textbox

              textboxsubcode.Text = dt.Rows[0][0].ToString();

              textboxsubname.Text = dt.Rows[0][1].ToString();

                cmboboxclass.Text = dt.Rows[0][2].ToString();

            }

            catch (Exception error)

            {

                MessageBox.Show(error.ToString());

            }

        }