phpBB : Critical Error

Error creating new session

DEBUG MODE

SQL Error : 1062 Duplicate entry '-1' for key 2

INSERT INTO phpbb_sessions (session_id, session_user_id, session_start, session_time, session_ip, session_page, session_logged_in, session_admin) VALUES ('b31d3491b5f03b90f7f8d9a2daf05829', -1, 1257606669, 1257606669, '266bbf63', 2, 0, 0)

Line : 234
File : sessions.php