I've searched and can't find a similar issue.
Just updated to 2.8.4. Now when I try to edit an existing post or when I try to publish a new post, it takes me to "Not Found - Sorry, you are looking for something that isn't here." page, like if I went to an incorrect url on my site.
When editing a post it shows in the address bar: http://www.url.com/wp-admin/post.php?action=edit&post=4725
When I try to publish a new post it shows in the address bar: http://www.url.com/wp-admin/post.php
Should there be a post.php in the wp-admin page? I don't have one.