Object Error leading to Deleted sims
Everything seemed normal for about 10 hours, when suddenly the game became EXTREMELY laggy (1 frame per minute) and I couldn't figure out why. It kept lagging for a while and then this window appear...
Forum Discussion
Do you have the debug cheat "boolprop testingcheatsenabled true" on? This can cause errors like this. So while the cheat is useful, it's best to use it for what you need then turn it off again, rather than have it permanently on.
PS I read you had played the game for 10 hours. With Sims 2, it's best to save regularly and also shut down and restart the game pretty regularly too, otherwise it starts to get cranky.
