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 ('379f30ba4a8e4893433a6c5fb0718e7e', -1, 1540220977, 1540220977, '3691534f', 3, 0, 0)

Line : 187
File : sessions.php