Unable to install modules with Drush
Drush 6 does not support Drupal 8 and you need to upgrade to drush 7 (well I just upgraded to drush 8):

Drush Version   :  8.0-dev


See duplicate issue: Running Drush returns an error

Edit: If you are working on Drupal 8 you need the Drupal Console its syntax is a bit long-winded, but it is incredibly powerful.