Comboboxcolumn datagridview c # sql server

I am working on a project on c # and sql server. When selecting an item from a comboboxcolumn, you must bring me the description and price from the database, if it does, but it marks the following error.

I have these events

private void dgtDVenta_EditingControlShowing(object sender, DataGridViewEditingControlShowingEventArgs e)
        {
            dgvCombo = e.Control as DataGridViewComboBoxEditingControl;

            if (dgvCombo != null)
            {
                dgvCombo.SelectedIndexChanged += new EventHandler(dgtDVenta_SelectedIndexChanged);
            }
        }
 private void dgtDVenta_CellEndEdit(object sender, DataGridViewCellEventArgs e)
        {
            if (dgvCombo != null)
                dgvCombo.SelectedIndexChanged -= new EventHandler(dgtDVenta_SelectedIndexChanged);

        }

private void dgtDVenta_SelectedIndexChanged(object sender, EventArgs e)
        {
            ComboBox combo = sender as ComboBox;
            cadena = "Server= " + serverName + ";Database= " + dataBase + " ;Trusted_Connection=True";
            string des;
            string precio;
            using (SqlConnection conn = new SqlConnection(cadena))
            {
                conn.Open();

                string sql = @"SELECT Descripcion_Prod, Precio FROM Producto WHERE IdProducto = @IdProducto";
                SqlCommand cmd = new SqlCommand(sql, conn);
                cmd.Parameters.AddWithValue("@IdProducto", combo.Text);
                adaptador = new SqlDataAdapter(cmd);
                tabla = new DataTable();
                adaptador.Fill(tabla);
                //des = Convert.ToString(cmd.ExecuteScalar());
                des = tabla.Rows[0]["Descripcion_Prod"].ToString();
                precio = tabla.Rows[0]["Precio"].ToString();
            }

            DataGridViewRow row = dgtDVenta.CurrentRow;
            row.Cells["Descripcion"].Value = des;
            row.Cells["Precio"].Value = precio;


        }