phpBB : Critical Error

Error creating new session

DEBUG MODE

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

INSERT INTO phpbb_sessions (session_id, session_user_id, session_start, session_time, session_ip, session_page, session_logged_in, session_admin) VALUES ('7ccd670b41de47c129c305ee159b86bc', -1, 1498343788, 1498343788, '369f6927', -1, 0, 0)

Line : 187
File : sessions.php