You are getting a 404 on CMS pages because of the remains of old store views still hanging around in the database after deleting store views from magneto admin, to clean up ( delete ) old unused CMS pages for store views you have deleted run this MySQL cmd.
DELETE FROM cms_page_store WHERE store_id NOT IN (SELECT store_id FROM core_store)
You could also use an app like phpmyadmin to manually look for CMS entries that have store IDs that you know not to be in use, but this could get messy.