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 ('2fe2718e64e2768ce96c420119d8a3e3', -1, 1411257619, 1411257619, '36a7607c', 0, 0, 0)

Line : 373
File : sessions.php