Excel report problem in c#

<pre lang="c#">using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using MySql.Data.MySqlClient;
using System.Runtime.InteropServices;
using iTextSharp.text;
using iTextSharp.text.pdf;
using iTextSharp.text.html;
using System.Diagnostics;
using iTextSharp.text.html.simpleparser;
using Microsoft.Office.Interop.Excel;
using System.Configuration;
using System.IO;
using System.Reflection;

namespace Billling_Machine
{
    public partial class Reports : Form
    {

        String ConnectionString = System.Configuration.ConfigurationManager.ConnectionStrings["myConnectionString"].ConnectionString;
        MySqlDataAdapter da;
        DataSet ds;
        
        public Reports()
        {
            InitializeComponent();
        }

        private void generate_Click(object sender, EventArgs e)
        {
            int datasetvalue;
            int datatablevalue;

         try
            {
               using(MySqlConnection con=new MySqlConnection(ConnectionString))
               {
              String query;

                StringBuilder queryBuilder = new StringBuilder();
                MySqlCommand command = new MySqlCommand();
                System.Data.DataTable dt = new System.Data.DataTable();
               
                string fromDate = dateTimePicker1.Value.ToString("yyyy-MM-dd");
                string toDate = dateTimePicker2.Value.ToString("yyyy-MM-dd");
                if ((reportsmachine.Text == "") && (reportscard.Text == "") &&(reportscustomer.Text==""))
                {
                    query = "select * from transaction where DATE(paid_date)BETWEEN '" + fromDate + "'AND '" + toDate + "' ";
                    da = new MySqlDataAdapter(query, con);
                    ds = new DataSet();
                  datasetvalue= da.Fill(ds);
                 
                   datatablevalue=da.Fill(dt);


                }

                else
                {
                    query = "select * from transaction where DATE(paid_date)BETWEEN '" + fromDate + "'AND '" + toDate + "' ";
                    if (reportsmachine.Text != "")
                    {
                        query = query + " AND " + "machine_id=" + "'" + reportsmachine.Text + "' ";
                    }
                    if (reportscustomer.Text != "")
                    {
                        query = query + " AND " + "customer_id=" + "'" + reportscustomer.Text + "' ";

                    }
                    if (reportscard.Text != "")
                    {
                        query = query + " AND " + "card_id=" + "'" + reportscard.Text + "' ";
                    }
                    
                    da = new MySqlDataAdapter(query, con);
                    ds = new DataSet();
                   datasetvalue = da.Fill(ds);

                    datatablevalue = da.Fill(dt);
                }
                if (datasetvalue != 0 && datatablevalue != 0)
                {
                    if (Convert.ToString(comboBox1.SelectedItem) == "EXCEL")
                    {
                        Microsoft.Office.Interop.Excel.Application excelApp = new Microsoft.Office.Interop.Excel.Application();


                        Microsoft.Office.Interop.Excel.Workbook workbook = (Microsoft.Office.Interop.Excel.Workbook)excelApp.Workbooks.Add(Missing.Value);

                        Microsoft.Office.Interop.Excel.Worksheet worksheet;


                        worksheet = (Microsoft.Office.Interop.Excel.Worksheet)workbook.Worksheets[1];

                        worksheet.Cells[1, 1] = "Machine ID";
                        worksheet.Cells[1, 2] = "Customer ID";
                        worksheet.Cells[1, 3] = "Card ID";
                        worksheet.Cells[1, 4] = "Name";
                        worksheet.Cells[1, 5] = "Address";
                        worksheet.Cells[1, 6] = "Phone No";
                        worksheet.Cells[1, 7] = "Item1 Name";
                        worksheet.Cells[1, 8] = "Item1 Rate";
                        worksheet.Cells[1, 9] = "Item1 Quantity";
                        worksheet.Cells[1, 10] = "Item1 Total";
                        worksheet.Cells[1, 11] = "Item2 Name";
                        worksheet.Cells[1, 12] = "Item2 Rate";
                        worksheet.Cells[1, 13] = "Item2 Quantity";
                        worksheet.Cells[1, 14] = "Item2 Total";
                        worksheet.Cells[1, 15] = "Item3 Name";
                        worksheet.Cells[1, 16] = "Item3 Rate";
                        worksheet.Cells[1, 17] = "Item3 Quantity";
                        worksheet.Cells[1, 18] = "Item3 Total";
                        worksheet.Cells[1, 19] = "Handling Cost";
                        worksheet.Cells[1, 20] = "Billed Amount";
                        worksheet.Cells[1, 21] = "Received Amount";
                        worksheet.Cells[1, 22] = "Paid Date";
                        worksheet.Cells[1, 23] = "Due Amount";

                        int row = 1;
                        for (int k = 1; k <= 23; k++)
                        {
                            worksheet.Cells[row, k].Interior.ColorIndex = 39;
                        }


                        string data = null;

                        int i = 0;

                        int j = 0;


                        for (i = 0; i <= ds.Tables[0].Rows.Count-1; i++)
                        {

                            for (j = 0; j <= ds.Tables[0].Columns.Count - 1; j++)
                            {

                                data = ds.Tables[0].Rows[i].ItemArray[j].ToString();

                                ((Microsoft.Office.Interop.Excel.Range)worksheet.Cells[i+2 , j + 1]).Value2 = data;

                            }

                        }

                        excelApp.Visible = true;



                    }//if}}