I've had this problem a few times too.
The first time, it was with a pregnant sim. I rebuilt the house and after I was finished, she couldn't enter. I tried moving the door, putting in more doors, but nothing worked apart from deleting a segment of wall. The second time, it was with the same sim (not pregnant this time) and her husband, neither could go inside. The kids could come and go without an issue though. I fixed it by travelling to the park with one of their kids and then switching control back to them. When I got back the issue was gone.