OP Generation Failed

Hi! I've also had this issue before when placing lots from the gallery and the way i fixed the issue was changing any and all platforms to ground level, effectively deleting them. For some reason it was interfering with the build; nothing else worked for me either, not going into manage worlds, not saving, not deleting any items, not even quiting the game entirely, super frustrating but thankfully easily solvable! Hope this helps for anyone else having this issue.

Hey! I just started a new save today. I put down a lot that I built on my old laptop, with no mods or CC and had moved my OG sim from their empty lot to that one. It was initially a cafe lot that I swapped to residential because I made it before the business and hobbies expansion. So I place my Sim in the lot and go to add some stairs to the third level to build him a unit and then I get an error that says "Op Generation Failed" tried it with some ladders, still failed but didn't give me a notification. 

I thought it might just be the lot, so I went to an empty lot in build mode: still got the error. Then tried to test out walls, to see if those would work. Sure do, but I went to click undo to erase the walls and undo button no longer works. Sledge Hammer does work on the first try but then stops working. 

Put down a bench, that works. Tried to move it? Won't place, no error message. 

Any ideas?

I went back on the OG lot and realized a lot of the items from the old save have been replaced or are white. Including a table that I have 9 of in the build in different colors. All but one is normal. Once again: this lot was built on vanilla no mods 

I checked a completely different save same issue. Also tried to repair the game. Nothing 

I'm having this issue right now :/ Did you find anything out? 

Same thing is happening to me with any kind of stairs edit. Adding a railing, placing stairs on porch or next floor, removing bottom of stairs, changing stairs color. It is rediculous!