^^ I was just thinking that while reading the problem. That way, once you enable debug mode an error box might pop up if there's a hack confliction/bug. You can choose delete, then exit/minimize your game, go to your
C:\My Documents\EA Games\The Sims 2\Logs folder, and find the name of the error log that appeared in the box. Then you can attach it to your post so that someone who can read those types of things figure out the cause of the problem. :angel:
Is time frozen on the lot along with the sims? And have you downloaded anything recently? You may have downloaded a few mods that are conflicting with each other, or you have one that's not compatible. From my experience, that's usually the case.

Also, have you tried the Sims 2 Hack Conflict Utility? You can find it over at
http://www.simwardrobe.com in the Sims 2 section.