As Lord St.Croix said, it's probably corrupted, so you might want to start over.

Make sure you read all the information available on Neighborhood and Game corruption, which can be found here:

http://simswiki.info/wiki.php%3Ftit...Hood_Corruption

http://sims.wikia.com/wiki/Game_gui...ding_corruption

Also, make sure you avoid touching/playing with certain Sims that aren't meant to be played with. Read this to help figure out who they are: http://sims.wikia.com/wiki/Game_gui...safe_to_play_as

Hope this helps!