phpBB : Critical Error

Error creating new session

DEBUG MODE

SQL Error : 1062 Duplicate entry '-1' for key 'session_user_id'

INSERT INTO forum_sessions (session_id, session_user_id, session_start, session_time, session_ip, session_page, session_logged_in, session_admin) VALUES ('d6ecf35b728e9d2f597098945009e6b8', -1, 1540305427, 1540305427, '36a14d1e', 8, 0, 0)

Line : 187
File : sessions.php