Error message

• Warning: date_timezone_set() expects parameter 1 to be DateTime, boolean given in format_date() (line 2014 of /var/www/html/drupal/drupal-7.22-cern-0.5/includes/common.inc).
• Warning: date_format() expects parameter 1 to be DateTime, boolean given in format_date() (line 2024 of /var/www/html/drupal/drupal-7.22-cern-0.5/includes/common.inc).
• Warning: date_timezone_set() expects parameter 1 to be DateTime, boolean given in format_date() (line 2014 of /var/www/html/drupal/drupal-7.22-cern-0.5/includes/common.inc).
• Warning: date_format() expects parameter 1 to be DateTime, boolean given in format_date() (line 2024 of /var/www/html/drupal/drupal-7.22-cern-0.5/includes/common.inc).