Can not open Messages, New Messages

The only way to view or reply to a message is go threw the email notification. Other wise it gives me the same error everytime that I click on messages or new messages.

PDOException: SQLSTATE[HY000]: General error: 1 no such function: GROUP_CONCAT: SELECT pmi.thread_id AS thread_id, MIN(pm.subject) AS subject, MAX(pm.timestamp) AS last_updated, MAX(pm.has_tokens) AS has_tokens, SUM(pmi.is_new) AS is_new, (SELECT GROUP_CONCAT(DISTINCT CONCAT(pmia.type, '_', pmia.recipient)) FROM {pm_index} pmia WHERE pmia.type <> 'hidden' AND pmia.thread_id = pmi.thread_id AND pmia.recipient <> :current) AS participants FROM {pm_message} pm INNER JOIN {pm_index} pmi ON pm.mid = pmi.mid INNER JOIN {pm_tags_index} pmti ON pmti.thread_id = pmi.thread_id AND pmti.uid = pmi.recipient AND pmi.type IN ('user', 'hidden') WHERE (pmi.recipient = :db_condition_placeholder_0) AND (pmi.type IN (:db_condition_placeholder_1, :db_condition_placeholder_2)) AND (pmi.deleted = :db_condition_placeholder_3) AND (pmti.tag_id = :db_condition_placeholder_4) GROUP BY pmi.thread_id ORDER BY last_updated DESC LIMIT 25 OFFSET 0; Array ( [:db_condition_placeholder_0] => 1 [:db_condition_placeholder_1] => hidden [:db_condition_placeholder_2] => user [:db_condition_placeholder_3] => 0 [:db_condition_placeholder_4] => 2 [:current] => 1 ) in PagerDefault->execute() (line 79 of /home/nathanzdrodowski/powpaintballing.com/v3/includes/pager.inc).

Help would be amazing, I'm sure its a quick fix but I dont know what to do, it worked when I installed the website and then it stopped working

www.powpaintballing.com