Drupal: "Site is offline for maintenance" message
I turned my website offline for maintenance and then logged out (or wanted to work on it from another computer).
All I got was the "Site is offline for maintenance message".
The Solution
Type the following address into your browser:
http://your-drupal-website.com/user
or
http://your-drupal-website.com/?=user
This will take you to the user login prompt - if you are the Administrator user you can then turn the site back online.