When I was creating one of the first dresses I ever created, I came to the problem that I didn't see the correct thumbnail. The thumbnail was different from the dress the sim was wearing.
I searched all over Google and MTS but didn't find the solution until I saw this page at TSR:
http://www.thesimsresource.com/tutorials/view/category//id/2575/bodyshop-tips-and-tricksThe trick is to delete this file:
CASThumbnails.packageRefresh BodyShop thumbnails. There are times when the thumbnailpreview doesn’t get updated for one reason or another. BodyShop thumbnailpreviews are stored in the following file: My Documents\EA Games\The Sims2\cigen.package. To refresh the previews simply delete that file. Next timeyou run BodyShop, it will create a blank cigen.package file forcing allthe previews to be generated again.
Refresh CAS screen thumbnails. Delete the following file: MyDocuments\EA Games\The Sims 2\Thumbnails\ CASThumbnails.package.Next time you run the game, the file will be recreated and the game forced togenerate all the thumbnail previews.
Don't worry about deleting it. When you start the game after deleting this file, the game will automaticly recreate this file and refresh it.