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 ('6c55b8a643880250f79107fd659ef6d8', -1, 1397737821, 1397737821, '6ca2d44b', -4, 0, 0)

Line : 187
File : sessions.php