Try to use the esc key. Maybe this works.
This is a known bug in the Mac version. It's been mentioned before in this forum - for example, #3 at the bottom of this post here
My question to Madrigan is - are you playing on a Mac laptop, or on a Mac desktop?
(It'd be nice to know if this is a bug issue that just effects laptops - I play on a Mac laptop, and I've occasionally encountered the 'Can't Save/Can't Hit ESC Button' bug...)
As to the issue, I hate to say it Madrigan, but you're going to have to quit the application and start your game over. I think there's no other way around this bug...
(The moral of this story is - once you get a game going, save often
, as you don't want to lose too much of your game if this bug hits again. And this bug will
hit again - it happens infrequently, but at random times...)