This was happening to me and I could not find how to access and edit my WP-filebase templates.
Then a found a forum post where they mention define('DISALLOW_FILE_EDIT', true); in the wp-config.php which is set by a security plugin. This is done in order to disable editing plugins from the admin area.
So I remembered that I had changed this myself for security reasons.
Set it to true if you have it as false and that should fix it.
It worked for me!
-Armando