Issue: If you have created a different pages for different store in CMS > Page and it is showing the Admin > Page > Manage Content > Error : Not Found you probably have removed some store from the admin.
Solution: The solution lies actually on cms_page_store table in the database. Example: You had a page_id of 2 (Home Page) that had entries for store id 1, 2 and 3. Since you deleted stores with ID of 2 and 3, those cms_page_store relations were no longer valid.
You simply removed the two missed entries from this table and now CMS/Manage Pages works properly in the admin. To do so just run in your database the following query:
DELETE FROM cms_page_store WHERE store_id NOT IN (SELECT store_id FROM core_store);
please note the name of the table.
Wish you success.