Drush not seeing right CLI PHP version
Have you just now updated your PHP than you may need to restart the apache and check if it works, and still if you get the above error than check Installing and Troubleshooting Drush.

One dirty hack of installing the drush is mentioned here: https://drupal.org/files/drush-document_env_var-1841324-25.patch. But I won't recommend you to use this as you are already having the PHP 5.4 and that hack for PHP version &lt; 5.3.3