I had this problem a while ago. I had like the 4th generation of a family that had just moved to Windenburg, and at first everything was fine, but then I kept getting the error whenever I tried to save. Plus whenever I tried to change anyone's appearance, my progress would resort to the last time I saved, but my sims appearance would stay changed.
It was getting so frustrating, so I came online to check for solutions, but found only that maybe moving your family would solve the problem. So I did. They were still in Windenburg, but on a different lot. And at first (while one of my sims was having a birthday party) i got the error again. But that was it. I have been playing for hours since then, moved my family again (this time to Newcrest), no errors since then, so idk what really fixed it.
But my guess was something with events, plus my clubs would just gather at random times (like during the night, when everyone was sleeping I'd get the message 'A club meeting has just started'), so I disbanded all my clubs (maybe that fixed it?)
Idk if this was helpful, but my friend is now having the same problem and moving the family didnt actually work for her. So Im hoping this issue will be fixed, since it can be really frustrating 🙂