The same thing happened on a client’s site – I backed up the site and the database and upgraded WordPress to 3.1.1 and also about a dozen plugins. Now the list of categories is not showing on Posts>Categories, but on the individual posts page it does not have anything in the list of “All Categories”, but it does have a list of categories on the “Most Used” tab. Even so, none of the posts are categorized; all were changed to uncategorized. Similarly, no posts have tags any more, but on the post page the list of tags shows up in the “Most Used” list.
This is a live client site, I’d rather not just start turning off plugins to trial and error my way through figuring out the problem, so if anyone can point me in the right direction that would help. The site is timothytaylorartist.com; and the categories are gone from the sidebar widgets that listed recent posts by category, and the navigation page that listed posts by category is showing nothing in the dropdown box either, so it’s a problem, not to mention we’d rather not retag and recategorize everything. The problem is, even if we had to recategorize etc; we wouldn’t be able to, because the lists of categories is not showing in the post page.
I’m using the Suffusion Theme, and a long list of plugins. Maybe we can compare notes?
