Toggle Hidden Units not working

[Blackcloud6]

I'm setting up Mentor Scenario 3 and try to hide the German units and it does not work.  The pull down for this is grayed out.  Could this be that I am playing solitaire?  It would still have a function to be able to show these hidden in solitaire, maybe a grayed out unit, as one could still play with the reduced spotting, otr to indicate a potential position one uses the full solitaire hidden units rules.