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 ('8b0973c41d7970174dd7c7d11c627f6b', -1, 1416673478, 1416673478, '36a1dca0', 16, 0, 0)

Line : 191
File : sessions.php