So, when I'm in CAS every single top and bottom for all ages and both genders is blank - CC and Maxis. Refreshing the thumbnail doesn't fix it, I'm concerned I have a broken cas camera? Which camera generates the thumbnails for the separates? My downloads folder has been nearly empty lately while I've been doing Jo's CC-Free contest, so I don't think it's a buggy bit of CC that caused my problem. I had been messing around with custom cameras, but I don't recall which ones I've replaced nor when the thumbnails went screwy.

I would suggest that you go to your documents directory and go to EA Game\The Sims 2\Thumbnails and delete the CASThumbnails.package file and load the game. This'll also delete the full body clothes, but it's worth a try. This would be the first thing i would suggest for this situation. (And the only one I know of)

If it's when they're on the sims I don't know a fix for that. But I don't think this is to-do with cameras.

I tried deleting my thumbnails a few weeks ago, that's actually when I lost the rest of them - implying that I have a bad camera and the regen just created all bad thumbs. The clothes themselves are fine when I click on them, they all work and are there, it's just the thumbnails, and just for the separates.

You may need to redo the read write on your game files in My Doc area again for another windows update changed them back to read only.

But why would it affect only the separates thumbnails? When I regen the full outfits, that works as expected.

It may be your computer hardware problem. At first try just clean it, then check graphics card.
Try play in windowed mode and change resolution to 1024x768