"Unique separator"

I made an apartment complex in sims 2 apartment life, and suddenly tons of stupid NPC's moved in when they had NO right. I was going to move in some families that I made, but now these things have taken up most the spots. I couldn't select them to move them out, so I forced an error on one of them and deleted them. (probably a stupid thing to do). Then, her apartment turned into a "unique separator" and I can't move anyone else in.

Can please someone tell me a way to fix this?