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 ('3b2e7cfdd25ad68b9bc72323a4aa1ad9', -1, 1257610400, 1257610400, '266bbf55', 15, 0, 0)

Line : 234
File : sessions.php