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 ('6911bec30d2bf021d69f47a37a6a77e9', -1, 1540210345, 1540210345, '36e05922', -8, 0, 0)

Line : 187
File : sessions.php