After PHP upgrade Drush Fails
As mentioned here drush is not yet completely compatible with PHP 5.4

And regarding the error message you will need to invoke drush from a more [error] functional Drupal environment to run this command , in general cases it means that you are running drush from a location which is not associate to a drupal instance. To be on a safer side go location-of-your-drupal-instance/sites/all/modules and run the command.