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 ('a1ca5d39a2d1b969fa4aa645f1e980d1', -1, 1537876473, 1537876473, '36a14757', 9, 0, 0)

Line : 187
File : sessions.php