404 error on new pages but only for non logged in users?

Question

So. Issue as title. Have researched lots but am near insanity!

1. Have done all the 'Refresh permalink' thing
2. Have edited .htaccess(*) and put generic rewrite code and refreshed permalinks again - the code gets overwritten with the original .htaccess rewrite code though in FTP the 'date modified' on the .htaccess file doesn't change (!??!)

Tried adding new menu and new page from scratch - this also returns 404 unless logged in as a user.

Any ideas please?

(*) Original .htaccess code replaced with:

    ># BEGIN WordPress
    ><IfModule mod_rewrite.c>
    >RewriteEngine On
    >RewriteBase /
    >RewriteRule ^index\.php$ - [L]
    >RewriteCond %{REQUEST_FILENAME} !-f
    >RewriteCond %{REQUEST_FILENAME} !-d
    >RewriteRule . /index.php [L]
    ></IfModule>
    ># END WordPress

...gets rewritten to:

  ># BEGIN WordPress
  ># The directives (lines) between "BEGIN WordPress" and "END WordPress" are
  ># dynamically generated, and should only be modified via WordPress filters.
  ># Any changes to the directives between these markers will be overwritten.
  ><IfModule mod_rewrite.c>
  >RewriteEngine On
  >RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization}] ##<--This line apparently gets added
  >RewriteBase /
  >RewriteRule ^index\.php$ - [L]
  >RewriteCond %{REQUEST_FILENAME} !-f
  >RewriteCond %{REQUEST_FILENAME} !-d
  >RewriteRule . /index.php [L]
  ></IfModule>
  ># END WordPress

Answer 1

Sorted!

.htaccess and permalinks NOT the issue.

Found it by disabling all plugins one by one until I found a content access restriction plug-in that had somehow been misconfigured for non logged in users. I hadn't changed anything but there we are! Reconfigured and back up and running.