This just happened to me. Sim had 3 different rental properties.
I have NO mods or CC, never did.
I was building a new rental property out when I got the error code trying to save.
I left the game without saving, when I re-launched it, the "resume" family was a completely different townie family never played before in another world altogether.
I then tried to load the last save of my actual active family, it would not load, just stayed on the loading screen forever.
I logged in again, used the resume on the townie family, then used manage worlds to return to my other family, except the only ones home were the dogs and it would not load.
I moved her out, then back in, then tried to sell all rental properties through the manage worlds. I was able to disconnect them all but lost the money and furnishings. Then I tried to buy the properties back. The one with tenants says I can't buy it or change it to a regular residential with tenants, but I also can't evict them because I don't own the lot, nobody does.
The other rental was vacant when I was building on it so I was able to go in and change it to residential, then buy it as just a lot, then change it back to residential rental. But now it won't let me do anything on it. I can't add units, I can't save I get the error message, and now I can't even sell it again when I try it just freezes.
I cannot upload a save file I have a custom built and do not use cloud services of any kind. I can email any save file if someone wants to provide me with an email to do so.
I also took my sim to buy residential rental property in a different world. It let me purchase the property but would not let me save (I tested it as soon as I was on property in build mode).
I have been playing fine for a few days, no issues. I had 7 units over 3 properties at maximum rents and then suddenly it all just went in the toilet for no reason.
