If you've never used one of the more recent simulations before, you need to start a new game, open the options dialog (F3), go to the Control tab, and untick the "Use Public Documents folder" checkbox.
The reason behind this is that your not supposed to put user-created files (like timetables, and saved simulations) into the Program Files folder, because writing access there requires Administrator rights.
So therefore, in the future Simsig will store these files in its own subfolder within the Public Documents directory, where you don't need any special permissions for write access.
The problem is that at the moment, if I'm not mistaken, the installer might install the timetable files into the Program Files directory regardless, in which case it might look like there is no timetable at all.