Drupal 6 to 7 upgrade: "PHP Fatal error: Unsupported operand types in /usr/share/drupal7/includes/common.inc"
The scenario is a Drupal 6 website running on Debian GNU/Linux current stable is upgraded to Drupal 7 from backports in order to test its behaviour once the new Debian stable is released and Drupal 6 becomes unavailable.
On the Drupal 6 website there is a menu link created as a short-cut to log a user in and take them to the home page. This hides away the huge login block.