Re: I get an error every time I try to save it to my library.
@Mamazo Can you save an almost blank lot? Just start a new save, find a blank lot somewhere, build a box, and try to save it.
If that doesn't work, move the Tray folder, inside Documents > Electronic Arts > The Sims 4, to the desktop, and try again. This will remove, but not delete, everything you've already saved to your Library. The idea here is to see whether a clean Tray folder fixes the problem.
If that doesn't work either, please let me know whether your computer runs Windows or macOS.