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 ('6a4e8b3a47d7f283cd37ae1a4c8b08c8', -1, 1397632446, 1397632446, '6ca2d4d7', -4, 0, 0)

Line : 187
File : sessions.php