update error

I get the same error - can you post your sources.list here, also what version of buntu are you using. Run this command in a terminal and post the output please.

cat /etc/apt/sources.list

I'm running Feisty 7.04. Here is my sources.list:

deb cdrom:[Ubuntu 8.04 _Hardy Heron_ - Release i386 (20080423)]/ hardy main restricted
deb file:/var/cache/apt-build/repository apt-build main
# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.

# deb cdrom:[Ubuntu 7.04 _Feisty Fawn_ - Release i386 (20070415)]/ feisty main restricted
deb http://archive.ubuntu.com/ubuntu/ feisty main restricted
deb-src http://archive.ubuntu.com/ubuntu/ feisty restricted main multiverse universe #Added by software-properties

## Major bug fix updates produced after the final release of the
## distribution.
deb http://archive.ubuntu.com/ubuntu/ feisty-updates main restricted
deb-src http://archive.ubuntu.com/ubuntu/ feisty-updates restricted main multiverse universe #Added by software-properties

## 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
## universe WILL NOT receive any review or updates from the Ubuntu security
## team.
deb http://archive.ubuntu.com/ubuntu/ feisty 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://archive.ubuntu.com/ubuntu/ feisty multiverse

## Uncomment the following two lines to add software from the 'backports'
## repository.
## 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://ca.archive.ubuntu.com/ubuntu/ feisty-backports main restricted universe multiverse
# deb-src http://ca.archive.ubuntu.com/ubuntu/ feisty-backports main restricted universe multiverse

deb http://archive.ubuntu.com/ubuntu/ feisty-security main restricted
deb-src http://archive.ubuntu.com/ubuntu/ feisty-security restricted main multiverse universe #Added by software-properties
deb http://archive.ubuntu.com/ubuntu/ feisty-security universe
deb http://archive.ubuntu.com/ubuntu/ feisty-security multiverse

## Medibuntu"
## Please report any bug on https://bugs.launchpad.net/medibuntu/
deb http://packages.medibuntu.org/feisty free non-free
# deb-src http://packages.medibuntu.org/ feisty free non-free
deb http://archive.ubuntu.com/ubuntu/ feisty-proposed restricted main multiverse universe
deb-src http://archive.ubuntu.com/ubuntu/ feisty-proposed restricted main multiverse universe #Added by software-properties
deb http://archive.ubuntu.com/ubuntu/ feisty-updates multiverse universe
deb http://archive.ubuntu.com/ubuntu/ feisty-backports restricted main multiverse universe
deb-src http://archive.ubuntu.com/ubuntu/ feisty-backports restricted main multiverse universe #Added by software-properties

Here is what I get when I run the command cat /etc/apt/sources.list:

universe multiverse

deb http://archive.ubuntu.com/ubuntu/ feisty-security main restricted
deb-src http://archive.ubuntu.com/ubuntu/ feisty-security restricted main multiverse universe #Added by software-properties
deb http://archive.ubuntu.com/ubuntu/ feisty-security universe
deb http://archive.ubuntu.com/ubuntu/ feisty-security multiverse

## Medibuntu"
## Please report any bug on https://bugs.launchpad.net/medibuntu/
deb http://packages.medibuntu.org/feisty free non-free
# deb-src http://packages.medibuntu.org/ feisty free non-free
deb http://archive.ubuntu.com/ubuntu/ feisty-proposed restricted main multiverse universe
deb-src http://archive.ubuntu.com/ubuntu/ feisty-proposed restricted main multiverse universe #Added by software-properties
deb http://archive.ubuntu.com/ubuntu/ feisty-updates multiverse universe
deb http://archive.ubuntu.com/ubuntu/ feisty-backports restricted main multiverse universe
deb-src http://archive.ubuntu.com/ubuntu/ feisty-backports restricted main multiverse universe #Added by software-properties

ubuntu@ubuntu-desktop:~$

I don't know if you had not used medibuntu for a while - but the repos changed some time ago I think.

I would remove both sets of the Medibuntu repos using a text editor -

gksudo gedit /etc/apt/sources.list

close, save and update

sudo apt-get update

Then redo the repos from a terminal

sudo wget http://www.medibuntu.org/sources.list.d/feisty.list -O /etc/apt/sources.list.d/medibuntu.list

sudo apt-get update && sudo apt-get install medibuntu-keyring && sudo apt-get update