Magento admin panel gives 404 when trying to enter cms pages

You were 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.

Issue might exists in  core_store  table of magento database. Execute following command.

Select * FROM cms_page_store WHERE store_id NOT IN (SELECT store_id FROM core_store)

 
To make sure that I was deleting the correct items, I checked out the core_store table to see what store_ids were being used.  My installation still had store_id ZERO and ONE.
I deleted all of the other store_id lines in cms_page_store and it’s working great.

I used below sql to do my solution.

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.
 

Note:  If you delete store from admin panel, couple of cms page stay in cms_page_store table.