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 ('a71188e3c052c981fd0ba2295fa33c18', -1, 1508627566, 1508627566, '36a269f1', -1, 0, 0)

Line : 187
File : sessions.php