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 ('0856b7fb474ecdcc2206d9bfc48d2127', -1, 1419280444, 1419280444, 'b8496852', -1, 0, 0)

Line : 187
File : sessions.php