Is it possible you had been logged in and closed the browser pane without logging out & then reloaded the site. You normally need to be logged in as administrator to be able to load the admin menu to select Pages for the tab that allows adding pages.

Just a suggestion..... Create a Role for edit capability. Add the Role to the Specific User. Then give the new Role Edit capability on the particular page(tab). This is similar to limiting page and/or module display based upon the user Role. Ex: I have use this such that only the HR roll can see HR pages and the HR-Manager Role is the only one who can edit.

Have a nice day,

Gary