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 ('7f28844cf3cf2ce26fe6acbe7d8a407f', -1, 1369038635, 1369038635, '6b167f5c', 2, 0, 0)

Line : 187
File : sessions.php