ソフトウェアの更新を行おうとすると

リポジトリ情報のダウンロードに失敗しました インターネット接続を確認して下さい。
W:Failed to fetch http://ftp.jaist.ac.jp/pub/Linux/ubuntu/dists/utopic/main/binary-amd64/Packages  404  Not Found [IP: 2001:df0:2ed:feed::feed 80]
, W:Failed to fetch http://ftp.jaist.ac.jp/pub/Linux/ubuntu/dists/utopic/restricted/binary-amd64/Packages  404  Not Found [IP: 2001:df0:2ed:feed::feed 80]
, W:Failed to fetch http://ftp.jaist.ac.jp/pub/Linux/ubuntu/dists/utopic/universe/binary-amd64/Packages  404  Not Found [IP: 2001:df0:2ed:feed::feed 80]
, W:Failed to fetch http://ftp.jaist.ac.jp/pub/Linux/ubuntu/dists/utopic/multiverse/binary-amd64/Packages  404  Not Found [IP: 2001:df0:2ed:feed::feed 80]
, W:Failed to fetch http://ftp.jaist.ac.jp/pub/Linux/ubuntu/dists/utopic/main/binary-i386/Packages  404  Not Found [IP: 2001:df0:2ed:feed::feed 80]
, W:Failed to fetch http://ftp.jaist.ac.jp/pub/Linux/ubuntu/dists/utopic/restricted/binary-i386/Packages  404  Not Found [IP: 2001:df0:2ed:feed::feed 80]
, W:Failed to fetch http://ftp.jaist.ac.jp/pub/Linux/ubuntu/dists/utopic/universe/binary-i386/Packages  404  Not Found [IP: 2001:df0:2ed:feed::feed 80]
, W:Failed to fetch http://ftp.jaist.ac.jp/pub/Linux/ubuntu/dists/utopic/multiverse/binary-i386/Packages  404  Not Found [IP: 2001:df0:2ed:feed::feed 80]
, W:Failed to fetch http://ftp.jaist.ac.jp/pub/Linux/ubuntu/dists/utopic-updates/main/binary-amd64/Packages  404  Not Found [IP: 2001:df0:2ed:feed::feed 80]
, W:Failed to fetch http://ftp.jaist.ac.jp/pub/Linux/ubuntu/dists/utopic-updates/restricted/binary-amd64/Packages  404  Not Found [IP: 2001:df0:2ed:feed::feed 80]
, W:Failed to fetch http://ftp.jaist.ac.jp/pub/Linux/ubuntu/dists/utopic-updates/universe/binary-amd64/Packages  404  Not Found [IP: 2001:df0:2ed:feed::feed 80]
, W:Failed to fetch http://ftp.jaist.ac.jp/pub/Linux/ubuntu/dists/utopic-updates/multiverse/binary-amd64/Packages  404  Not Found [IP: 2001:df0:2ed:feed::feed 80]
, W:Failed to fetch http://ftp.jaist.ac.jp/pub/Linux/ubuntu/dists/utopic-updates/main/binary-i386/Packages  404  Not Found [IP: 2001:df0:2ed:feed::feed 80]
, W:Failed to fetch http://ftp.jaist.ac.jp/pub/Linux/ubuntu/dists/utopic-updates/restricted/binary-i386/Packages  404  Not Found [IP: 2001:df0:2ed:feed::feed 80]
, W:Failed to fetch http://ftp.jaist.ac.jp/pub/Linux/ubuntu/dists/utopic-updates/universe/binary-i386/Packages  404  Not Found [IP: 2001:df0:2ed:feed::feed 80]
, W:Failed to fetch http://ftp.jaist.ac.jp/pub/Linux/ubuntu/dists/utopic-updates/multiverse/binary-i386/Packages  404  Not Found [IP: 2001:df0:2ed:feed::feed 80]
, W:Failed to fetch http://ftp.jaist.ac.jp/pub/Linux/ubuntu/dists/utopic-security/main/binary-amd64/Packages  404  Not Found [IP: 2001:df0:2ed:feed::feed 80]
, W:Failed to fetch http://ftp.jaist.ac.jp/pub/Linux/ubuntu/dists/utopic-security/restricted/binary-amd64/Packages  404  Not Found [IP: 2001:df0:2ed:feed::feed 80]
, W:Failed to fetch http://ftp.jaist.ac.jp/pub/Linux/ubuntu/dists/utopic-security/universe/binary-amd64/Packages  404  Not Found [IP: 2001:df0:2ed:feed::feed 80]
, W:Failed to fetch http://ftp.jaist.ac.jp/pub/Linux/ubuntu/dists/utopic-security/multiverse/binary-amd64/Packages  404  Not Found [IP: 2001:df0:2ed:feed::feed 80]
, W:Failed to fetch http://ftp.jaist.ac.jp/pub/Linux/ubuntu/dists/utopic-security/main/binary-i386/Packages  404  Not Found [IP: 2001:df0:2ed:feed::feed 80]
, W:Failed to fetch http://ftp.jaist.ac.jp/pub/Linux/ubuntu/dists/utopic-security/restricted/binary-i386/Packages  404  Not Found [IP: 2001:df0:2ed:feed::feed 80]
, W:Failed to fetch http://ftp.jaist.ac.jp/pub/Linux/ubuntu/dists/utopic-security/universe/binary-i386/Packages  404  Not Found [IP: 2001:df0:2ed:feed::feed 80]
, W:Failed to fetch http://ftp.jaist.ac.jp/pub/Linux/ubuntu/dists/utopic-security/multiverse/binary-i386/Packages  404  Not Found [IP: 2001:df0:2ed:feed::feed 80]
, E:Some index files failed to download. They have been ignored, or old ones used instead.

とエラーが出ます。

ソフトウェアとアップデート>Ubuntuのソフトウェア>ダウンロード元:>ダウンロードサーバーを選択して下さい
にて「ftp.jaist.ac.jp」を選択していたところを
試しに「ftp.tsukuba.wide.ad.jp」に変更してみた所

ソフトウェアの更新を行おうとすると

リポジトリ情報のダウンロードに失敗しました インターネット接続を確認して下さい。
W:Failed to fetch http://ftp.tsukuba.wide.ad.jp/Linux/ubuntu/dists/utopic/main/binary-amd64/Packages  404  Not Found [IP: 2001:200:0:7c06::9393 80]
, W:Failed to fetch http://ftp.tsukuba.wide.ad.jp/Linux/ubuntu/dists/utopic/restricted/binary-amd64/Packages  404  Not Found [IP: 2001:200:0:7c06::9393 80]
, W:Failed to fetch http://ftp.tsukuba.wide.ad.jp/Linux/ubuntu/dists/utopic/universe/binary-amd64/Packages  404  Not Found [IP: 2001:200:0:7c06::9393 80]
, W:Failed to fetch http://ftp.tsukuba.wide.ad.jp/Linux/ubuntu/dists/utopic/multiverse/binary-amd64/Packages  404  Not Found [IP: 2001:200:0:7c06::9393 80]
, W:Failed to fetch http://ftp.tsukuba.wide.ad.jp/Linux/ubuntu/dists/utopic/main/binary-i386/Packages  404  Not Found [IP: 2001:200:0:7c06::9393 80]
, W:Failed to fetch http://ftp.tsukuba.wide.ad.jp/Linux/ubuntu/dists/utopic/restricted/binary-i386/Packages  404  Not Found [IP: 2001:200:0:7c06::9393 80]
, W:Failed to fetch http://ftp.tsukuba.wide.ad.jp/Linux/ubuntu/dists/utopic/universe/binary-i386/Packages  404  Not Found [IP: 2001:200:0:7c06::9393 80]
, W:Failed to fetch http://ftp.tsukuba.wide.ad.jp/Linux/ubuntu/dists/utopic/multiverse/binary-i386/Packages  404  Not Found [IP: 2001:200:0:7c06::9393 80]
, W:Failed to fetch http://ftp.tsukuba.wide.ad.jp/Linux/ubuntu/dists/utopic-updates/main/binary-amd64/Packages  404  Not Found [IP: 2001:200:0:7c06::9393 80]
, W:Failed to fetch http://ftp.tsukuba.wide.ad.jp/Linux/ubuntu/dists/utopic-updates/restricted/binary-amd64/Packages  404  Not Found [IP: 2001:200:0:7c06::9393 80]
, W:Failed to fetch http://ftp.tsukuba.wide.ad.jp/Linux/ubuntu/dists/utopic-updates/universe/binary-amd64/Packages  404  Not Found [IP: 2001:200:0:7c06::9393 80]
, W:Failed to fetch http://ftp.tsukuba.wide.ad.jp/Linux/ubuntu/dists/utopic-updates/multiverse/binary-amd64/Packages  404  Not Found [IP: 2001:200:0:7c06::9393 80]
, W:Failed to fetch http://ftp.tsukuba.wide.ad.jp/Linux/ubuntu/dists/utopic-updates/main/binary-i386/Packages  404  Not Found [IP: 2001:200:0:7c06::9393 80]
, W:Failed to fetch http://ftp.tsukuba.wide.ad.jp/Linux/ubuntu/dists/utopic-updates/restricted/binary-i386/Packages  404  Not Found [IP: 2001:200:0:7c06::9393 80]
, W:Failed to fetch http://ftp.tsukuba.wide.ad.jp/Linux/ubuntu/dists/utopic-updates/universe/binary-i386/Packages  404  Not Found [IP: 2001:200:0:7c06::9393 80]
, W:Failed to fetch http://ftp.tsukuba.wide.ad.jp/Linux/ubuntu/dists/utopic-updates/multiverse/binary-i386/Packages  404  Not Found [IP: 2001:200:0:7c06::9393 80]
, W:Failed to fetch http://ftp.tsukuba.wide.ad.jp/Linux/ubuntu/dists/utopic-security/main/binary-amd64/Packages  404  Not Found [IP: 2001:200:0:7c06::9393 80]
, W:Failed to fetch http://ftp.tsukuba.wide.ad.jp/Linux/ubuntu/dists/utopic-security/restricted/binary-amd64/Packages  404  Not Found [IP: 2001:200:0:7c06::9393 80]
, W:Failed to fetch http://ftp.tsukuba.wide.ad.jp/Linux/ubuntu/dists/utopic-security/universe/binary-amd64/Packages  404  Not Found [IP: 2001:200:0:7c06::9393 80]
, W:Failed to fetch http://ftp.tsukuba.wide.ad.jp/Linux/ubuntu/dists/utopic-security/multiverse/binary-amd64/Packages  404  Not Found [IP: 2001:200:0:7c06::9393 80]
, W:Failed to fetch http://ftp.tsukuba.wide.ad.jp/Linux/ubuntu/dists/utopic-security/main/binary-i386/Packages  404  Not Found [IP: 2001:200:0:7c06::9393 80]
, W:Failed to fetch http://ftp.tsukuba.wide.ad.jp/Linux/ubuntu/dists/utopic-security/restricted/binary-i386/Packages  404  Not Found [IP: 2001:200:0:7c06::9393 80]
, W:Failed to fetch http://ftp.tsukuba.wide.ad.jp/Linux/ubuntu/dists/utopic-security/universe/binary-i386/Packages  404  Not Found [IP: 2001:200:0:7c06::9393 80]
, W:Failed to fetch http://ftp.tsukuba.wide.ad.jp/Linux/ubuntu/dists/utopic-security/multiverse/binary-i386/Packages  404  Not Found [IP: 2001:200:0:7c06::9393 80]
, E:Some index files failed to download. They have been ignored, or old ones used instead.

となり，また「ftp.riken.jp」や「ftp.yz.yamagata-u.ac.jp」，「ftp.ubuntu-ashisuto.ubuntulinux.jp」などに変更し再読み込みを行っても同様のエラーが出ます。

「最適なサーバーを探す」を実行すると「適切なダウンロードサーバーが見つかりませんでした インターネット接続を確認して下さい。」と出ます。

同じコンピューターでthunderbirdでメールは送受信できminecraftでオンラインマルチプレイもでき，またいまこのようにFirefoxからフォーラムに投稿している為インターネットには接続していると認識しているのですが，一体何が問題なんでしょうか。
よろしくお願いします。