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 ('40e436fcd86d4ce2e1a18efe13dfa216', -1, 1406827933, 1406827933, '36c4b56d', 0, 0, 0)

Line : 373
File : sessions.php