To make the sim able to enter the house all I did was delete the ceiling tiles. It was a clean game on a secondary account that had nothing but the CEP and the CC that came with the house. It was definitely the ceiling tiles preventing my sim from entering, because as soon as I deleted a few tiles, the piece of ground/house floor below became available. I didn't delete any plants or any items from the foyer, etc. Only ceiling tiles. Once the tiles were gone, the sim could walk around the house. I don't know why, but that really does seem to be the problem in this case.
That's odd. Never happened to me before. But thanks for sharing. I'll have to keep this in mind