My sources.list contains the following:
```
deb mirror://mirrors.ubuntu.com/mirrors.txt precise main restricted universe multiverse
deb mirror://mirrors.ubuntu.com/mirrors.txt precise-updates main restricted universe multiverse
deb mirror://mirrors.ubuntu.com/mirrors.txt precise-backports main restricted universe multiverse
deb mirror://mirrors.ubuntu.com/mirrors.txt precise-security main restricted universe multiverse
deb-src mirror://mirrors.ubuntu.com/mirrors.txt precise main restricted universe multiverse
deb-src mirror://mirrors.ubuntu.com/mirrors.txt precise-updates main restricted universe multiverse
deb-src mirror://mirrors.ubuntu.com/mirrors.txt precise-backports main restricted universe multiverse
deb-src mirror://mirrors.ubuntu.com/mirrors.txt precise-security main restricted universe multiverse
```
When I run aptitude update, I see the following errors:
```
Err mirror://mirrors.ubuntu.com precise-backports/main Sources
No mirror file '/var/lib/apt/mirrors/mirrors.ubuntu.com_mirrors.txt' found [Mirror: ]
Err mirror://mirrors.ubuntu.com precise-backports/restricted Sources
No mirror file '/var/lib/apt/mirrors/mirrors.ubuntu.com_mirrors.txt' found [Mirror: ]
Err mirror://mirrors.ubuntu.com precise-backports/universe Sources
No mirror file '/var/lib/apt/mirrors/mirrors.ubuntu.com_mirrors.txt' found [Mirror: ]
Err mirror://mirrors.ubuntu.com precise-backports/multiverse Sources
No mirror file '/var/lib/apt/mirrors/mirrors.ubuntu.com_mirrors.txt' found [Mirror: ]
Err mirror://mirrors.ubuntu.com precise-backports/main amd64 Packages
No mirror file '/var/lib/apt/mirrors/mirrors.ubuntu.com_mirrors.txt' found [Mirror: ]
Err mirror://mirrors.ubuntu.com precise-backports/restricted amd64 Packages
No mirror file '/var/lib/apt/mirrors/mirrors.ubuntu.com_mirrors.txt' found [Mirror: ]
Err mirror://mirrors.ubuntu.com precise-backports/universe amd64 Packages
No mirror file '/var/lib/apt/mirrors/mirrors.ubuntu.com_mirrors.txt' found [Mirror: ]
Err mirror://mirrors.ubuntu.com precise-backports/multiverse amd64 Packages
No mirror file '/var/lib/apt/mirrors/mirrors.ubuntu.com_mirrors.txt' found [Mirror: ]
Err mirror://mirrors.ubuntu.com precise-backports/main i386 Packages
No mirror file '/var/lib/apt/mirrors/mirrors.ubuntu.com_mirrors.txt' found [Mirror: ]
Err mirror://mirrors.ubuntu.com precise-backports/restricted i386 Packages
No mirror file '/var/lib/apt/mirrors/mirrors.ubuntu.com_mirrors.txt' found [Mirror: ]
Err mirror://mirrors.ubuntu.com precise-backports/universe i386 Packages
No mirror file '/var/lib/apt/mirrors/mirrors.ubuntu.com_mirrors.txt' found [Mirror: ]
Err mirror://mirrors.ubuntu.com precise-backports/multiverse i386 Packages
No mirror file '/var/lib/apt/mirrors/mirrors.ubuntu.com_mirrors.txt' found [Mirror: ]
```
ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: apt-cacher-ng 0.7.2-1ubuntu1
ProcVersionSignature: Ubuntu 3.2.0-26.41-generic 3.2.19
Uname: Linux 3.2.0-26-generic x86_64
ApportVersion: 2.0.1-0ubuntu8
Architecture: amd64
Date: Wed Jul 4 18:53:04 2012
InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Beta amd64 (20120328)
ProcEnviron:
TERM=screen-256color
PATH=(custom, user)
LANG=fi_FI.UTF-8
SHELL=/bin/zsh-beta
SourcePackage: apt-cacher-ng
UpgradeStatus: No upgrade log present (probably fresh install)
Status changed to 'Confirmed' because the bug affects multiple users.