I noticed for version 1.8.0 I made a mistake that can cause category layouts to invalidate when you save them.
This is fixed for 1.8.1. However, once your layout was invalidated, it will stay invalidated even after you update to 1.8.1.
Everybody who has this problem can write an email with their wordpress admin panel login data to: email@example.com
I will fix this issue for everybody and restore your layouts! Then, everything will work fine again with 1.8.1.
Sorry for the inconvenience! :(