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 ('cd516df7c71ece8cd366d68c8344cd9c', -1, 1440746707, 1440746707, '365a850a', -1, 0, 0)

Line : 187
File : sessions.php