I’m getting this exact same error, except it happens when a category-restricted user tries to post a new article. I’ve looked through at least 50 threads on related topics, and none of them have been any help at all.
Even though there’s an error, the post still goes through.
I am also using the Role Manager plugin, as well as the default Akismet and Backup plugins. But I have the latest version of everything, so that’s not the problem.