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 ('ff8879711f4d38fe080d61eccce5e1dc', -1, 1540033294, 1540033294, '36c637a7', -4, 0, 0)

Line : 189
File : sessions.php