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 ('071e46a6cd171d6d091b8b7816166d21', -1, 1474959524, 1474959524, '32131f63', -1, 0, 0)

Line : 187
File : sessions.php