Running Drush returns an error I am running Drush version 6.2.0 and the latest Drupal 8 beta on Dreamhosters. When I run drush cc all within the sites directory, I receive the following error immediately after executing the command:


  Fatal error: Class 'Drupal\Core\Session\AccountInterface' not found in 
      /home/mywebsite/mywebsite.com/core/includes/bootstrap.inc on line 63
      Drush command terminated abnormally due to an unrecoverable error.                                                                            





  Error: Class 'Drupal\Core\Session\AccountInterface' not found in
      /home/mywebsite/mywebsite.com/core/includes/bootstrap.inc, line 63


Why does it happen? How can I fix this?
Drush 6 does not support Drupal 8.  You must use drush 7.0-rc1 with Drupal 8 beta 9, or drush master head with Drupal 8 head.

UPDATE: Drush 7 no longer supports Drupal 8; now, use Drush 8 with Drupal 8.