WordPress is giving you an unexpected error ‘404 – Page not found’ ? And you are sure this page should exist?
Most likely this is a problem with the permalink structure.
The good news: That’s easy to fix:
Go to Settings → Permalinks and klick the >b>Save button. This will flush the permalink structure and should fix your problem.
By the way: I recommend using a permalink structure using the post name, ie day and name, month and name or post name.