private void ImportThread()
        {
            _timetable = _importer.ImportTimetable();
            Invoke(new MethodInvoker(delegate
            {
                if (_timetable != null)
                {
                    // build relational data
                    _timetable.BuildEquivalency();
                    _timetable.BuildCompatibility();

                    Next();
                }
                else
                {
                    MessageBox.Show("Failed to import timetable data.", "Import",
                                    MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
                    Close();
                }
            }));
        }