Vanishing Signals

I have laid out a circuit based on Cincinnati Ohio, With runs out to outlying towns.
The route uses new and old existing track plus imaginary lines to form a Metro type run and freight from industry in the area.
I used signals from SMM USS NS and everything was fine for about three weeks of work.
Now I have lost the signals.
The track links are still there but no signals. There is a milk bottle where the physical sign should be,
when I select it, the popout shows all the details of the signal, even my setting of 10 for the visual part.
Does any one have any ideas?
The route uses new and old existing track plus imaginary lines to form a Metro type run and freight from industry in the area.
I used signals from SMM USS NS and everything was fine for about three weeks of work.
Now I have lost the signals.
The track links are still there but no signals. There is a milk bottle where the physical sign should be,
when I select it, the popout shows all the details of the signal, even my setting of 10 for the visual part.
Does any one have any ideas?