You'll see the message 'Page Not Available' when a page has been hidden.
SpinSite allows site administrators to flag a page as 'Hidden' via the Page Options dialog (accessed from the Page Options button in the top right hand corner of your page). When a page is hidden it can only be viewed by someone logged in as an administrator. In addition, a hidden page will not show up on the navigation.
To un-Hide a page, you must log into your site, navigate to that page, and choose 'Page Options' button at the top of your screen. From there you'll see that the 'Hide This Page' option under visibility has been selected. (You will need to un-select it.)