Hi,
I had already done that last time I updated and it worked then but I didn't realise I would have to do that each time....
Just tried it and it didn't work unfortunately.
# apt update
Hit
http://security.debian.org testing/updates Release.gpg
Ign
http://security.debian.org/ testing/updates/contrib Translation-en
Ign
http://security.debian.org/ testing/updates/contrib Translation-en_GB
Hit
http://ftp.debian.org testing Release.gpg
Ign
http://ftp.debian.org/debian/ testing/contrib Translation-en
Ign
http://ftp.debian.org/debian/ testing/contrib Translation-en_GB
Hit
http://www.lamaresh.net squeeze Release.gpg
Ign
http://www.lamaresh.net/apt/ squeeze/main Translation-en
Ign
http://www.lamaresh.net/apt/ squeeze/main Translation-en_GB
Get:1
http://packages.linuxmint.com debian Release.gpg [198 B]
Ign
http://packages.linuxmint.com/ debian/import Translation-en
Ign
http://packages.linuxmint.com/ debian/import Translation-en_GB
Ign
http://packages.linuxmint.com/ debian/main Translation-en
Ign
http://security.debian.org/ testing/updates/main Translation-en
Ign
http://security.debian.org/ testing/updates/main Translation-en_GB
Ign
http://security.debian.org/ testing/updates/non-free Translation-en
Ign
http://security.debian.org/ testing/updates/non-free Translation-en_GB
Hit
http://security.debian.org testing/updates Release
Hit
http://www.debian-multimedia.org testing Release.gpg
Ign
http://www.debian-multimedia.org/ testing/main Translation-en
Ign
http://www.debian-multimedia.org/ testing/main Translation-en_GB
Ign
http://ftp.debian.org/debian/ testing/main Translation-en
Ign
http://ftp.debian.org/debian/ testing/main Translation-en_GB
Ign
http://ftp.debian.org/debian/ testing/non-free Translation-en
Ign
http://ftp.debian.org/debian/ testing/non-free Translation-en_GB
Hit
http://ftp.debian.org testing Release
Hit
http://security.debian.org testing/updates/main i386 Packages
Ign
http://packages.linuxmint.com/ debian/main Translation-en_GB
Ign
http://packages.linuxmint.com/ debian/upstream Translation-en
Ign
http://packages.linuxmint.com/ debian/upstream Translation-en_GB
Get:2
http://packages.linuxmint.com debian Release [6,532 B]
Hit
http://ftp.debian.org testing/main i386 Packages/DiffIndex
Hit
http://security.debian.org testing/updates/contrib i386 Packages
Hit
http://security.debian.org testing/updates/non-free i386 Packages
Ign
http://www.debian-multimedia.org/ testing/non-free Translation-en
Ign
http://www.debian-multimedia.org/ testing/non-free Translation-en_GB
Hit
http://www.debian-multimedia.org testing Release
Hit
http://www.lamaresh.net squeeze Release
Hit
http://ftp.debian.org testing/contrib i386 Packages/DiffIndex
Hit
http://ftp.debian.org testing/non-free i386 Packages/DiffIndex
Ign
http://packages.linuxmint.com debian/main i386 Packages
Ign
http://www.lamaresh.net squeeze/main i386 Packages
Hit
http://www.debian-multimedia.org testing/main i386 Packages/DiffIndex
Ign
http://packages.linuxmint.com debian/import i386 Packages
Ign
http://www.lamaresh.net squeeze/main i386 Packages
Hit
http://www.debian-multimedia.org testing/non-free i386 Packages/DiffIndex
Ign
http://packages.linuxmint.com debian/upstream i386 Packages
Hit
http://www.lamaresh.net squeeze/main i386 Packages
Ign
http://packages.linuxmint.com debian/main i386 Packages
Ign
http://packages.linuxmint.com debian/import i386 Packages
Ign
http://packages.linuxmint.com debian/upstream i386 Packages
Hit
http://packages.linuxmint.com debian/main i386 Packages
Hit
http://packages.linuxmint.com debian/import i386 Packages
Hit
http://packages.linuxmint.com debian/upstream i386 Packages
Fetched 6,730 B in 5s (1,197 B/s)
Reading package lists... Done
N: Ignoring file 'opera.list.save' in directory '/etc/apt/sources.list.d/' as it has an invalid filename extension
N: Ignoring file 'boxee.list.save' in directory '/etc/apt/sources.list.d/' as it has an invalid filename extension
N: Ignoring file 'google-chrome.list.save' in directory '/etc/apt/sources.list.d/' as it has an invalid filename extension
# sudo rm /var/lib/dpkg/info/mintdesktop.prerm
rm: cannot remove `/var/lib/dpkg/info/mintdesktop.prerm': No such file or directory
# apt install mintdesktop
Reading package lists... Done
Building dependency tree
Reading state information... Done
mintdesktop is already the newest version.
The following package was automatically installed and is no longer required:
icoutils
Use 'apt-get autoremove' to remove them.
0 upgraded, 0 newly installed, 0 to remove and 72 not upgraded.
N: Ignoring file 'opera.list.save' in directory '/etc/apt/sources.list.d/' as it has an invalid filename extension
N: Ignoring file 'boxee.list.save' in directory '/etc/apt/sources.list.d/' as it has an invalid filename extension
N: Ignoring file 'google-chrome.list.save' in directory '/etc/apt/sources.list.d/' as it has an invalid filename extension