That happened to me once when I had discovered the joys of the testingcheatsenabled cheat code. I used it to give one of my sims the grey mannequin skintone, which didn't have the genetic information for children coded into it, and consequently made my game crash when she was about to give birth.
there is a mod for grey mannequin skintone its at modthesims2.com
its does not affect any EP its Compatible with inteen
http://modthesims.info/download.php?t=292423but you have to Register first to get the download