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 ('df83690b22bc8948f492d9cda3c77966', -1, 1529873346, 1529873346, '36e05bf6', -4, 0, 0)

Line : 187
File : sessions.php