Magento admin display "404 error: Page not found." when I'm trying to enter CMS/Pages in the navigation. All other pages work great and even other items in CMS menu, only Pages gives 404. What should I do?
Had this exact problem..
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 magento 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.
Original source: http://www.magentocommerce.com/boards/viewthread/18223/