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 ('15a76cb0a1b32d9bc67fddde1ad8e22e', -1, 1257632078, 1257632078, '266bbf59', 8, 0, 0)

Line : 234
File : sessions.php