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) VALUES ('a40194ecc0dce0e1bdda330ce45a6a77', -1, 1490328840, 1490328840, 'ac44417d', -6, 0)

Line : 158
File : sessions.php