I've been so thrilled with Atahualpa, except for one major problem: if you clicked through on the categories list, you got nothing. Zip. Nada.
I was mystified. Why did the category ID number show up on mouse-over, but the page was empty when clicked? Everything looked normal in the Dashboard. I could assign a category to new posts, make new categories, etc.
Then I started to wonder about plugins and conflicts. I deactivated several of the many plugins that seemed to relate to categories, and I found the culprit. It does not play well with this theme! Stay away from Ultimate Category Excluder. It's supposed to let you decide where certain categories won't show up, but it made all of mine disappear from the menu!