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 ('8721f0d573d3b6745a9bef89b47626c0', -1, 1480955903, 1480955903, '369e773c', 26, 0, 0)

Line : 172
File : sessions.php