Ubuntu 12.04.5 LTSを使用していますが、最近apt-get updateが失敗するようになってしまいました。
/var/lib/apt/listsを削除したり、apt-get cleanを実行したりしましたが状況は変わりません。
何が原因でしょうか？
sudo apt-get updateの実行結果と、/etc/apt/sources.listの内容は以下のとおりです。
他に必要な情報があればご連絡ください。

よろしくお願いいたします。

【sudo apt-get update時のアウトプット】
Get:1 http://security.ubuntu.com precise-security Release.gpg [198 B]
Get:2 http://us.archive.ubuntu.com precise Release.gpg [198 B]
Get:3 http://security.ubuntu.com precise-security Release [55.5 kB]
Get:4 http://security.ubuntu.com precise-security/main Sources [142 kB]
Get:5 http://security.ubuntu.com precise-security/restricted Sources [4,476 B]
Get:6 http://security.ubuntu.com precise-security/universe Sources [3,339 B]
Get:7 http://security.ubuntu.com precise-security/multiverse Sources [208 B]
100% [7 Sources bzip2 0 B] [Waiting for headers] [Waiting for headers]bzip2: (stdin) is not a bzip2 file.
Get:8 http://security.ubuntu.com precise-security/main amd64 Packages [199 B]
100% [8 Packages bzip2 0 B] [Waiting for headers] [Waiting for headers]bzip2: (stdin) is not a bzip2 file.
Get:9 http://security.ubuntu.com precise-security/restricted amd64 Packages [202 B]
100% [9 Packages bzip2 0 B] [Waiting for headers] [Waiting for headers]bzip2: (stdin) is not a bzip2 file.
Get:10 http://security.ubuntu.com precise-security/universe amd64 Packages [205 B]
100% [10 Packages bzip2 0 B] [Waiting for headers] [Waiting for headers]bzip2: (stdin) is not a bzip2 file.
Get:11 http://security.ubuntu.com precise-security/multiverse amd64 Packages [2,573 B]
100% [11 Packages bzip2 0 B] [Waiting for headers] [Waiting for headers]bzip2: (stdin) is not a bzip2 file.
Get:12 http://security.ubuntu.com precise-security/main i386 Packages [774 kB]
100% [12 Packages bzip2 0 B] [Waiting for headers]                                                             34.0 kB/s 0sbzip2: (stdin) is not a bzip2 file.
Get:13 http://security.ubuntu.com precise-security/restricted i386 Packages [18.3 kB]
100% [13 Packages bzip2 0 B] [Waiting for headers]                                                             34.0 kB/s 0sbzip2: (stdin) is not a bzip2 file.
Get:14 http://security.ubuntu.com precise-security/universe i386 Packages [168 kB]
100% [14 Packages bzip2 0 B] [Waiting for headers]                                                             34.0 kB/s 0sbzip2: (stdin) is not a bzip2 file.
Get:15 http://security.ubuntu.com precise-security/multiverse i386 Packages [2,980 B]
100% [15 Packages bzip2 0 B] [Waiting for headers]                                                             34.0 kB/s 0sbzip2: (stdin) is not a bzip2 file.
Get:16 http://security.ubuntu.com precise-security/main TranslationIndex [850 kB]
E: Unable to parse package file /var/lib/apt/lists/partial/security.ubuntu.com_ubuntu_dists_precise-security_main_i18n_Index (1)

【/etc/apt/sources.listの内容】
# deb http://us.archive.ubuntu.com/ubuntu/ precise main restricted

# deb http://us.archive.ubuntu.com/ubuntu/ precise-updates main restricted
# deb http://security.ubuntu.com/ubuntu precise-security main restricted

# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
deb http://us.archive.ubuntu.com/ubuntu/ precise main restricted
deb-src http://us.archive.ubuntu.com/ubuntu/ precise main restricted

## Major bug fix updates produced after the final release of the
## distribution.
deb http://us.archive.ubuntu.com/ubuntu/ precise-updates main restricted
deb-src http://us.archive.ubuntu.com/ubuntu/ precise-updates main restricted

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team. Also, please note that software in universe WILL NOT receive any
## review or updates from the Ubuntu security team.
deb http://us.archive.ubuntu.com/ubuntu/ precise universe
deb-src http://us.archive.ubuntu.com/ubuntu/ precise universe
deb http://us.archive.ubuntu.com/ubuntu/ precise-updates universe
deb-src http://us.archive.ubuntu.com/ubuntu/ precise-updates universe

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team, and may not be under a free licence. Please satisfy yourself as to
## your rights to use the software. Also, please note that software in
## multiverse WILL NOT receive any review or updates from the Ubuntu
## security team.
deb http://us.archive.ubuntu.com/ubuntu/ precise multiverse
deb-src http://us.archive.ubuntu.com/ubuntu/ precise multiverse
deb http://us.archive.ubuntu.com/ubuntu/ precise-updates multiverse
deb-src http://us.archive.ubuntu.com/ubuntu/ precise-updates multiverse

## N.B. software from this repository may not have been tested as
## extensively as that contained in the main release, although it includes
## newer versions of some applications which may provide useful features.
## Also, please note that software in backports WILL NOT receive any review
## or updates from the Ubuntu security team.
deb http://us.archive.ubuntu.com/ubuntu/ precise-backports main restricted universe multiverse
deb-src http://us.archive.ubuntu.com/ubuntu/ precise-backports main restricted universe multiverse

deb http://security.ubuntu.com/ubuntu precise-security main restricted
deb-src http://security.ubuntu.com/ubuntu precise-security main restricted
deb http://security.ubuntu.com/ubuntu precise-security universe
deb-src http://security.ubuntu.com/ubuntu precise-security universe
deb http://security.ubuntu.com/ubuntu precise-security multiverse
deb-src http://security.ubuntu.com/ubuntu precise-security multiverse

## Uncomment the following two lines to add software from Canonical's
## 'partner' repository.
## This software is not part of Ubuntu, but is offered by Canonical and the
## respective vendors as a service to Ubuntu users.
# deb http://archive.canonical.com/ubuntu precise partner
# deb-src http://archive.canonical.com/ubuntu precise partner

## Uncomment the following two lines to add software from Ubuntu's
## 'extras' repository.
## This software is not part of Ubuntu, but is offered by third-party
## developers who want to ship their latest software.
# deb http://extras.ubuntu.com/ubuntu precise main
# deb-src http://extras.ubuntu.com/ubuntu precise main