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 ('f38c337c3340d1c35aeaa4e5c2a4bda9', -1, 1529754748, 1529754748, '36901087', -8, 0, 0)

Line : 187
File : sessions.php