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 ('8fe1bc6fcd80adc5bbf59e3aa08aa8f7', -1, 1529873207, 1529873207, '36e05bf6', 6, 0, 0)

Line : 187
File : sessions.php