Check the Thumbnails folder under 'The Sims 2' -- I believe there's a file there for Bodyshop. Just delete it and BS will regenerate it when it needs to.
In My Documents? I've deleted everything in there. I did find another file in Program Files\The Sims 2\TSData\Res\UserData, but I don't know if this is used - the modify date is just off the cd, and it has some thumbnails in for things like face templates, which don't show up anywhere in my actual game as they've been replaced (they show up properly in Bodyshop, too!) :/
Have you used CTRL + Right click on the thumbnails in CAS?
I might try this 'cause I'm all out of ideas and this can't hurt. But in CAS, they already have properly-updated thumbnails. It's just a Bodyshop problem.
Have you replaced the thumbnail swatch?
Makeup doesn't automatically generate thumbnails, you have to create them.
Yeah, I replaced them, they show up fine in CAS - I just can't get them to show up in Bodyshop