Error message

PDOException: SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry 'PHPMailer-class' for key 1: INSERT INTO {registry} (name, type, filename, module, weight) VALUES (:db_insert_placeholder_0, :db_insert_placeholder_1, :db_insert_placeholder_2, :db_insert_placeholder_3, :db_insert_placeholder_4), (:db_insert_placeholder_5, :db_insert_placeholder_6, :db_insert_placeholder_7, :db_insert_placeholder_8, :db_insert_placeholder_9); Array ( [:db_insert_placeholder_0] => PHPMailer [:db_insert_placeholder_1] => class [:db_insert_placeholder_2] => sites/all/libraries/phpmailer/class.phpmailer.php [:db_insert_placeholder_3] => phpmailer [:db_insert_placeholder_4] => 0 [:db_insert_placeholder_5] => phpmailerException [:db_insert_placeholder_6] => class [:db_insert_placeholder_7] => sites/all/libraries/phpmailer/class.phpmailer.php [:db_insert_placeholder_8] => phpmailer [:db_insert_placeholder_9] => 0 ) in _registry_parse_file() (line 179 of /home/content/89/6787389/html/drupal/includes/registry.inc).

How do I fix this?