phpBB : Critical Error

Error creating new session

DEBUG MODE

SQL Error : 1062 Duplicate entry '-1' for key 'session_user_id'

INSERT INTO phpbb_sessions (session_id, session_user_id, session_start, session_time, session_ip, session_page, session_logged_in, session_admin) VALUES ('b07db894fd939b44ea5f4ae8cb60d249', -1, 1406637761, 1406637761, '3652aadf', 7, 0, 0)

Line : 180
File : sessions.php