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 ('6fb8d536f69a5d482c66945f41b29271', -1, 1540302487, 1540302487, '36e09618', -8, 0, 0)

Line : 921
File : sessions.php