I'll take a look later today
EDIT:
@ckovel2000 Your save is HUGE. Are you actually playing with all these families ? I don't know if there's any save game bloating going on for you. I'm assuming that it's a probably too big and your computer is running into some kind of memory issue so that the lots can't be loaded anymore.
I'll forward your save to the devs but I fear all you can do for the moment, is try to reduce the file size. Maybe mark families you're not playing as not played, reduce inventories, reduce relationships, ...
I've loaded one of your lots and the RAM usage is at 4 GB. How much RAM do you have ?