Replace Repositories (Ubuntu)

sudo gedit /etc/apt/sources.list

Replace everything with the following list:
## Add comments (##) in front of any line to remove it from being checked.
## Use the following sources.list at your own risk.


deb http://archive.ubuntu.com/ubuntu dapper main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu dapper main restricted universe multiverse


## MAJOR BUG FIX UPDATES produced after the final release
deb http://archive.ubuntu.com/ubuntu dapper-updates main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu dapper-updates main restricted universe multiverse


## UBUNTU SECURITY UPDATES
deb http://security.ubuntu.com/ubuntu dapper-security main restricted universe multiverse
deb-src http://security.ubuntu.com/ubuntu dapper-security main restricted universe multiverse


## BACKPORTS REPOSITORY (Unsupported. May contain illegal packages. Use at own risk.)
deb http://archive.ubuntu.com/ubuntu dapper-backports main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu dapper-backports main restricted universe multiverse


## PLF REPOSITORY (Unsupported. May contain illegal packages. Use at own risk.)
deb http://packages.freecontrib.org/plf dapper free non-free
deb-src http://packages.freecontrib.org/plf dapper free non-free


## CANONICAL COMMERCIAL REPOSITORY (Hosted on Canonical servers, not Ubuntu
## servers. RealPlayer10, Opera and more to come.)
deb http://archive.canonical.com/ubuntu dapper-commercial main

Then, update your repositories:
sudo apt-get update