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I have this happen when my Sims attend a party. I'm not sure if it's something new or if it's always been like this. It's like you can't do anything on a house when your Sims are already inside, even if it's only one of your Sims. However, if you go to the inside of the house, any Sim in your household can interact with the other Sims or with anything inside the house.
Also, would you please change the subject of this thread to something that's more specific? What you have now doesn't give any real information about what you're asking and it makes it harder for people who are browsing around the Forum.
Lastly, I'm moving this over to the Miscellaneous Help board.