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 ('174e77cf1978ddbf6a398287518bf09c', -1, 1467366608, 1467366608, '1714fc4b', 0, 0, 0)

Line : 201
File : sessions.php