Hi Jude,
I see a few suggestions as I searched for this problem.
- Try a test of saving a different house to see if it saves.
- Have you tried saving it again with a different name?
- Try saving the house while being logged out of the game.
- Move the Mods folder out, and try saving the house again.
You said you tried this?:
- Make a new Sims 3 folder, load saved game. Then try saving the house.
Hope this helps
MrsFlynn