Try dragging the contents of your Thumbnails folder to a safe place on your hard drive. The game will (slowly) regenerate them, and CAS should look ok again.
Why drag them somewhere to keep them? They regenerate, just delete them. Keeping those would kind of be like keeping a copy of the .cache file that you are about the delete.
The catalog will be a little slower the first time going through it after deleting the thumbnails. You could also use Ctrl and right click on the pictures to regenerate a thumbnail.
On the odd chance that it's something causing the game to crash before it gets around to reading the thumbnails, you can put them back and try something else independently. I rename the cache files too, instead of deleting them.
Better still, delete the thumbnails folder- that way the game just fetches a copy from the install files, so you don't have to wait for all of the Maxis thumbs to regenerate- just your CC.
Thanks! I'll recommend people drag out the whole Thumbnails folder instead of just the contents.