Cannot select category from edit page

After upgrading from 2.0.2 to 2.1, I have this error on the wp-admin/post.php page (when editing or creating a new post):

WordPress database error: [Unknown column 'link_count' in 'where clause']
SELECT cat_ID FROM wp_categories WHERE category_parent = 0 AND ( link_count = 0 OR category_count != 0 OR ( link_count = 0 AND category_count = 0 ) ) ORDER BY category_count DESC

Is there any solution for this? Thanks. I can access the categories page and edit the categories, add new ones, etc. with no problem.