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 ('991a3aed50e45d73f4bb6625654f0ab8', -1, 1513245453, 1513245453, '36a3d16d', -4, 0, 0)

Line : 192
File : sessions.php