phpBB : Critical Error

Error creating new session

DEBUG MODE

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

INSERT INTO phpbb2_sessions (session_id, session_user_id, session_start, session_time, session_ip, session_page, session_logged_in, session_admin) VALUES ('c85a8e2e0ed7a84142e9f2f7b1f4d451', -1, 1269172959, 1269172959, '266bbf55', -4, 0, 0)

Line : 187
File : sessions.php