Hi, I also am getting the error when I try to load the game. I may have found a workaround, but it is not ideal...
I played the game in the past while logged into a standard user account on my PC. I tried to play the game again recently, and learned of the error. I tested logging out of my standard user account on the PC and into the administrator account (kept distinct from all other regular users for security reasons) and I was able to play the game (but none of the old city saves yet; I'm guessing that should be possible to copy around in explorer). This setup is not ideal however because playing in the admin account kind of defeats that security measure.
So from what I experienced this seems to be more of a Windows security issue rather than an issue with the game? I know we have seen suggestions to "right click and run as admin", and those types of things, but I guess maybe there is some other layer of authentication occurring while the game is loading to check if the user is an admin or not? Hopefully the results of my testing give someone smarter than me a clue of how we may be able to fix this issue in a good way.