First try going to tiki-admin_system.php page and clearing the /temp/cache/. You should now see four permissions on category permissions pages. In which case you need to verify that your registered user group has tiki_p_view_categorized and tiki_p_edit_categorized for each appropriate category.
Alternatively, you can give those permissions globally to the registered users group, as a whole, if it's the same for most categories. But note that the changes won't propagate to the existing categories (that I know of), so you'll have to verify the permissions of each category.