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 ('c8d53d0bf8f8a8a9a4dc2fdb8bd4ee88', -1, 1540205894, 1540205894, '36e0387e', 7, 0, 0)

Line : 187
File : sessions.php