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 ('551bfffba78d7e0ca9e3fe775a22dde2', -1, 1498169071, 1498169071, '36e0b483', 7, 0, 0)

Line : 189
File : sessions.php