Ideas
i downloaded a community space lot from the gallery to Willow Creek (it had no votes yet). my save was new and completely mod-free. i placed the community space lot while my active sim was on the lot. at first, everything seemed fine, but once i traveled with my sim, the game gave me an error code (The game failed to load. Error Code: 123:35e4f805:f2e2fcc8. It is recommended that you
relaunch the game.). i was still able to enter build mode from manage worlds, so i thought maybe the issue was with some of the furniture and deleted a few items. however, the problem didn’t change.
while in build mode, i could see that the lot requirements for all versions (Community Space, Maker Space, Garden, and Market) were fulfilled. but when i returned to manage worlds, the lot had a warning symbol like it was still incomplete or missing requirements. i ended up deleting the entire lot, and since then, the error hasn't come back.