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 ('71abd07eba7c5d50b48a30fd51419d40', -1, 1466934773, 1466934773, '36a13465', -1, 0, 0)

Line : 187
File : sessions.php