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 ('206e993546b7cc1eb200cae4abf080c1', -1, 1493423328, 1493423328, '36e0cf0d', -1, 0, 0)

Line : 187
File : sessions.php