I was recently having an issue where SP 2013 users with Full Control of a site would receive a page access error when trying to edit the page.
To fix this you need to give users proper access to the page layouts and master pages.
Go to the top level of the site then:
Site settings > Master pages and page layouts
View the “Library Settings” and then the “Permissions for this document library”. In my case, this library had unique permissions and only a special admin group had access. Set the permissions to inherit and it should then fix the issue.