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 ('bf7e6bb3aca208e5a17a699ddf4bba3b', -1, 1537603479, 1537603479, '3650537b', 7, 0, 0)

Line : 187
File : sessions.php