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 ('6d0a875e46012d9a84a64d4177fd13a5', -1, 1440905329, 1440905329, '3692f86f', -1, 0, 0)

Line : 187
File : sessions.php