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 ('781d76ba41e6c7a14107b5820aac7965', -1, 1263425892, 1263425892, '42f941ee', 20, 0, 0)

Line : 187
File : sessions.php