private void ax_OnAttTransactionEx(object sender, Axzkemkeeper._IZKEMEvents_OnAttTransactionExEvent e)
        {
           //....         
        }

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;

namespace Threading.UI.Winforms
{
    public partial class BackgroundWorkerBadExample : Form
    {
        public BackgroundWorkerBadExample()
        {
            InitializeComponent();
        }

        private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
        {
            try
            {
                for (int i = 0; i < (int)e.Argument; i++)
                {
                    txtResults.Text += string.Format(
                        "processing {0}\r\n", i.ToString());
                }
            }
            catch (InvalidOperationException oex)
            {
                MessageBox.Show(oex.Message);
            }

        }

        private void backgroundWorker1_RunWorkerCompleted(object sender, 
            RunWorkerCompletedEventArgs e)
        {
            MessageBox.Show("Completed background task");
        }

        private void btnGo_Click(object sender, EventArgs e)
        {
            backgroundWorker1.RunWorkerAsync(100);
        }
    }
}