phpBB : Critical Error

Error creating new session

DEBUG MODE

SQL Error : 1062 Duplicate entry '-1' for key 'session_user_id'

INSERT INTO sessions (session_id, session_user_id, session_start, session_time, session_ip, session_page, session_logged_in, session_admin) VALUES ('64e4e7ac5ece6ad7b5aed604444c3db0', -1, 1422841456, 1422841456, '36a1b3da', 0, 0, 0)

Line : 187
File : sessions.php