Although featured as 2.2/2.1 compatible by me, “Cats Drop Down” doesn’t work with WP 2.1 or 2.2 yet, only with 2.3. I will have a fixed version online within a couple days, need to finish my newest theme first which is almost done.
I am also in the process of changing my internal setup and this site here to allow for better/faster theme testing, downloads, ratings etc. You’ll be able to test all themes online, just like now, but additionally in 2.2 and 2.1, and on a huge sample site with all kinds of posts, comments, pages, categories.
Just to let you know that a lot of good WP stuff is going to be released here, so stay tuned.