The ability to refresh the thumbnail previews in the game catalog is very useful, especially if you are a creator. It is well known, generated thumbnail views are stored in My Documents\EA Games\The Sims 2\Thumbnails\ folder. If you delete all the files in there, the game will recreate them again.

Here is a new trick to refresh thumbnail previews in BodyShop. I was working on hair mesh when I traced the previews to the file called cigen.package. The file is located in My Documents\EA Games\The Sims 2\ folder. Delete the file and run the BodyShop, the file will be recreated and all the previews generated anew.