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, is_robot, session_admin) VALUES ('0b5edcfcf6a8ae43802054a200ac750a', -1, 1454856841, 1454856841, '36a702c8', 6, 0, '0', 0)

Line : 174
File : sessions.php