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 ('37537c301098f8d6a76c4d4124249b39', -1, 1413845066, 1413845066, '36d3d4ae', -1, 0, 0)

Line : 187
File : sessions.php