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 ('6810d7b765c3e7c72da7c0cb127e09dd', -1, 1516784975, 1516784975, '36ea414e', 1, 0, 0)

Line : 189
File : sessions.php