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 ('ff2aa6835de71e34d9b3a012936944d1', -1, 1418949102, 1418949102, '36a6ffa8', 45, 0, 0)

Line : 169
File : sessions.php