private void tCMain_Selecting(object sender, TabControlCancelEventArgs e) { if (UnitSet.GetClients().Count <= 1) { return; } if (2 == e.TabPageIndex || 3 == e.TabPageIndex) { DialogHelper.ShowError("Please select only one client for Conformance testing.\r\n" + "If you need to consider identified clients as a single system, please follow these steps:\r\n" + "1. Select multiple clients in the list using either Shift or Ctrl\r\n" + "2. Right click on selection and select Merge option"); e.Cancel = true; } }