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 ('3d9d2c765d822a05c10b682d76d78f9f', -1, 1524177820, 1524177820, '365174bb', -4, 0, 0)

Line : 187
File : sessions.php