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 ('72f4d00afe35abd4f95b10efef5b6206', -1, 1406387372, 1406387372, '36c68c82', 9, 0, 0)

Line : 180
File : sessions.php