I've installed a number of blogs but have never ran into this. Logged in as my admin user, I try to add / remove categories, comments, etc etc and I receive an error saying 'You don't have permission to do that'. This is a fresh install (which reported no errors).
I've attempted to create other users with admin / editor / etc but logged in as any of them, I still receive the same errors, regardless of account type. Any ideas anyone?