Problem with Sims 3?

I'm having a problem with the game. Whenever I tell my Sim to do something, he'll disappear and then reappear somewhere else in the house. If I tell him to eat, he'll get the food and all, and just as he's about to eat, the food will disappear, and then he will disappear as well and reappear somewhere else. So he can't eat, shower, sleep, or anything, and his stats are decreasing. He can go to work, visit someone's house, and walk around, but he can't eat, sleep, or shower. Even if he goes to someone else's house, once I tell him to do one of those things, he will disappear from their house and reappear at his house. I have another Sim in the same household as him who doesn't have any problem. How can I fix this?