C#

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Diagnostics;
using System.Drawing;
using System.Linq;
using System.Runtime.InteropServices;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace Klikacz____TzPw
{

    public partial class Form1 : Form
    {
        [DllImport(dllName: "User32.dll", CharSet = CharSet.Auto, CallingConvention = CallingConvention.StdCall)]

        public static extern void mouse_event(int dwFlags, int dx, int dy, int cButtons, int dwExtraInfo);

        private const int LEFTUP = 0x0004;
        private const int LEFTDOWN = 0x0002;

        public Form1()
        {
            InitializeComponent();
            this.ActiveControl = button1;
            button1.Focus();
        }

        private void Click_clock_Tick(object sender, EventArgs e)
        {
            Random rnd = new Random();
            int maxcps = (int)Math.Round(1000.0 / (trackBar1.Value + 0 * 0.2));
            int mincps = (int)Math.Round(1000.0 / (trackBar1.Value + 0 * 0.4));

            try
            {
                Click_clock.Interval = rnd.Next(mincps, maxcps);
            }

            catch
            {
                //Ignored..
            }

            bool mousdown = MouseButtons == MouseButtons.Left;
            if (mousdown)
            {
                mouse_event(dwFlags: LEFTUP, dx: 0, dy: 0, cButtons: 0, dwExtraInfo: 0);
                Thread.Sleep(millisecondsTimeout: rnd.Next(1, 6));
                mouse_event(dwFlags: LEFTDOWN, dx: 0, dy: 0, cButtons: 0, dwExtraInfo: 0);
            }

        }

        private void button1_Click(object sender, EventArgs e)
        {
            if (button1.Text.Contains("Uruchom"))
            {
                Click_clock.Start();
                button1.Text = "Wstrzymaj";
            }
            else
            {
                Click_clock.Stop();
                button1.Text = "Uruchom";
            }
        }

        private void trackBar1_Scroll(object sender, EventArgs e)
        {
            CPSValue.Text = "CPS = " + trackBar1.Value.ToString();
        }
    }
}

// insert at Class scope in your UserControl or sub-classed WinForm container

protected override CreateParams CreateParams
{
    get
    {
        CreateParams cp = base.CreateParams;
        cp.ExStyle = cp.ExStyle | 0x2000000;
        return cp;
    }
}

        database db = new database();        DataTable tbl = new DataTable();
        private void AutoNumber()
        {
            tbl.Clear();
            tbl = db.readData("Select max (Des_ID) from Deserved", "");


// in the next line the error coming out


            if ((tbl.Rows[0][0].ToString() == DBNull.Value.ToString()))
            {
                txtID.Text = "1";
            }
            else
            {
                txtID.Text = (Convert.ToInt32(tbl.Rows[0][0]) + 1).ToString();
            }
            NudPrice.Value = 1;
            DtbDate.Text = DateTime.Now.ToShortDateString();
            txtNotes.Clear();
            btnAdd.Enabled = true;
            btnNew.Enabled = true;
            btnDelete.Enabled = false;
            btnDeleteAll.Enabled = false;
            btnSave.Enabled = false;