Sims won't go upstairs

Every time I try to have my sims go upstairs, or do an activity upstairs (sleep, shower, etc.), they won't do it because they say they can't go there. Even when I click on the floor itself, it won't even bring up go here, job here, or anything. It just shows my mouse and the two feet. I've even tried rebuilding the stairs, moving lights, adding and removing fences and walls. I also removed my mods, thinking that might be the issue. I also tried bulldozing the lot and replacing it. I don't know what to do or try anymore.