I just started to have this issue when I updated to 3.1 from 3.0.1. I had some custom post types for a car dealer website. And as you may figured it out already, I used taxonomies (a.k.a. "Categories") to arrange the cars by Brand, Car Type, and just that. So, I created 2 kinds of custom taxonomies.
It all went good and was already working in my sandbox, and later in the actual production server. But now, when I auto-updated (never will do it again. Lesson learned), the editing of the custom taxonomies thrown an error telling me at the very best Nelson-from-the-simpsons-style: "Cheatin', huh? ha ha", when I didn't even set up the capabilities. It was doing cool without the capabilities, so I though "well, maybe for security reasons, now WP wants me to set up the capabilities for sure". I did it, and tried all available, but nothing happens, and I still have the problem.
I had to hack the
wp-admin/edit-tags.php and comment the line of the function
die();but I know this is foolish and I need a solution I can implement into the content folder, and not editing the core files.
I don't think is my fault, since in 3.0.1 it just worked fine. And for the record, the categories from the "Posts" sections are just working fine. Kinda funny since they use the same
edit-tags.php file to make the edition.
Ok crew. Thanks in advance for the help. Will wait for answers. :)