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 ('65ec2b7cc61595afac0a631b5cb496a8', -1, 1425192588, 1425192588, '365cff40', 45, 0, 0)

Line : 169
File : sessions.php