Site guest users trying to access salesforce standard pages in Force.com sites
|Knowledge Article Number||000213455|
|Resolution||"Force.com sites only deal with VisualForce pages and not standard pages"
Even if the object has all the required permissions, when you try to access the site,
You will be able to access First_Page, but once you click the link to standard salesforce page, you will be redirected to "Authorization Required" or "Page Under Construction" pages.
Users with guest user license will not be able to access standard salesforce pages using force.com sites.
In force.com sites, users should create a custom VF page and add it to the site accessible VF pages list.