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 ('981dbaba9d5fcd2e7fbd7ee15f6adbfe', -1, 1269219453, 1269219453, '266bbf59', -6, 0, 0)

Line : 187
File : sessions.php