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 ('8868a5e8bd17d46adeb2ef2cc136968a', -1, 1430003551, 1430003551, '36a67a45', 5, 0, 0)

Line : 189
File : sessions.php