There is already an open datareader associated with this command which must be closed first

private void btnSave_Click(object sender, EventArgs e)
        {
            if (txtFlavorName.Equals("") && cboSupplier.Text.Equals(""))
            {
                MessageBox.Show("Please make sure that you have entered a flavor name and selected the corresponding supplier.", "", MessageBoxButtons.OK, MessageBoxIcon.Warning);
                return;
            }

            else
            {
                try
                {
                    bool flavorExists = false;
                    int supplierid = 0;
                    //Get supplier Id

                    string query = "SELECT supplier_id FROM tbl_suppliers WHERE supplier_co_name = @supplier_name";
                    using (SqlConnection con = new SqlConnection(connstring))
                    {
                        con.Open();
                        using (SqlTransaction trans = con.BeginTransaction())
                        {
                            using (SqlCommand cmd = new SqlCommand(query, con))
                            {
                                cmd.Transaction = trans;
                                SqlDataReader reader;
                                cmd.Parameters.AddWithValue("@supplier_name", cboSupplier.Text.ToString());
                                reader = cmd.ExecuteReader();
                                if (reader.Read())
                                {
                                    supplierid = Convert.ToInt32(reader["supplier_id"].ToString());
                                }
                                reader.Close();
                            }
                        }
                    }

                    //Verify if flavor already exists
                    query = "SELECT * FROM TBL_FLAVORS WHERE flavor_name = @flavor_name AND flavor_supplierid = @supplier_id";
                    using (SqlConnection con = new SqlConnection(connstring))
                    {
                        con.Open();
                        using (SqlTransaction trans = con.BeginTransaction())
                        {
                            using (SqlCommand cmd = new SqlCommand(query, con))
                            {
                                cmd.Transaction = trans;
                                SqlDataReader read;
                                cmd.Parameters.AddWithValue("@flavor_name", txtFlavorName.Text.ToString());
                                cmd.Parameters.AddWithValue("@supplier_id", supplierid);
                                read = cmd.ExecuteReader();
                                if (read.Read())
                                {
                                    MessageBox.Show("This flavor for this supplier already exists.");
                                    return;
                                }
                                read.Close();
                            }
                            trans.Commit();
                        }
                    }
                    //
                    query = "INSERT INTO tbl_flavors (flavor_name, flavor_supplierid) VALUES (@flavor_name, @supplier_id)";
                    using (SqlConnection con = new SqlConnection(connstring))
                    {
con.Open();
                        using (SqlTransaction trans = con.BeginTransaction())
                        {
                            using (SqlCommand cmd = new SqlCommand(query, con))
                            {
                                cmd.Transaction = trans;
                                cmd.Parameters.AddWithValue("@flavor_name", txtFlavorName.Text.ToString());
                                cmd.Parameters.AddWithValue("@supplier_id", supplierid);
                                cmd.ExecuteNonQuery();
                            }
                            trans.Commit();
                        }
                    }
                }
                catch (Exception ex)
                {
                    MessageBox.Show(ex.ToString());
                }
            }
        }