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 ('a88f6616c636db71ee6d39fcee7af17a', -1, 1540302693, 1540302693, '36a14d1e', 5, 0, 0)

Line : 187
File : sessions.php