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 ('360fbfa45ee13ee047acb04a7b9eb052', -1, 1397855240, 1397855240, '36518159', -9, 0)

Line : 158
File : /forum/includes/sessions.php