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 ('435c1dcbea65b2f5afa9ead9d07d3950', -1, 1284150968, 1284150968, '266bbf6f', 18, 0, 0)

Line : 187
File : sessions.php