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 ('109b3966b498ea13c5b2e41a76f52ea1', -1, 1455202470, 1455202470, '36523bb6', 5, 0, 0)

Line : 189
File : sessions.php