private void OnViewerSelected(object sender, EventArgs e)
        {
            ComboBoxItemWithEntity serviceItem = (ComboBoxItemWithEntity)viewer.comboBoxService.SelectedItem;

            if (serviceItem == null)
            {
                Util.ShowErrorDialog(UtnEmall.ServerManager.Properties.Resources.NoServiceSelected);
                return;
            }

            if (statistics != null && statistics.IsVisible)
            {
                Util.ShowErrorDialog(UtnEmall.ServerManager.Properties.Resources.ServiceStatisticsViewerOpened);
                return;
            }

            statistics = new ServiceStatistics((ServiceEntity)serviceItem.Entity, control.Session);
            statistics.ShowDialog();
        }