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 ('2a31260129940fb0766f2f9217aa66e4', -1, 1427767189, 1427767189, '36a7afee', -1, 0, 0)

Line : 187
File : sessions.php