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 ('6609a6fcd230aa6f9c10d46e6ad8b8cd', -1, 1422209792, 1422209792, '3691a121', -9, 0, 0)

Line : 189
File : sessions.php