I just did a demo installation of Synaptic from Kub. Live CD and got 
these error messages after entering "sudo apt-get install synaptic" 

--- 

Get:1 http://archive.ubuntu.com/ubuntu/ precise/main sgml-data all 2.0.6 [271 kB ] 

Get:2 http://archive.ubuntu.com/ubuntu/ precise/main docbook-xml all 4.5-7ubuntu 1 [336 kB] 

Get:3 http://archive.ubuntu.com/ubuntu/ precise/main python-gnupginterface all 0 .3.2-9.1ubuntu3 [19.2 kB] 

Get:4 http://archive.ubuntu.com/ubuntu/ precise/main libvte-common all 1:0.28.2- 3ubuntu2 [22.8 kB] 

Get:5 http://archive.ubuntu.com/ubuntu/ precise/main libvte9 i386 1:0.28.2-3ubun tu2 [372 kB] 

Get:6 http://archive.ubuntu.com/ubuntu/ precise/main python-pkg-resources all 0. 6.24-1ubuntu1 [63.1 kB] 

Get:7 http://archive.ubuntu.com/ubuntu/ precise-updates/main unattended-upgrades all 0.76ubuntu1 [24.7 kB] 

Get:8 http://archive.ubuntu.com/ubuntu/ precise/main python-pycurl i386 7.19.0-4 ubuntu3 [48.5 kB] 

Get:9 http://archive.ubuntu.com/ubuntu/ precise/main librarian0 i386 0.8.1-5 [59 .2 kB] 

Get:10 http://archive.ubuntu.com/ubuntu/ precise/main rarian-compat i386 0.8.1-5 [104 kB] 

Get:11 http://archive.ubuntu.com/ubuntu/ precise/main python-defer all 1.0.2+bzr 481-1 [10.9 kB] 

Get:12 http://archive.ubuntu.com/ubuntu/ precise-updates/main python-aptdaemon a ll 0.43+bzr805-0ubuntu9 [82.2 kB] 

Get:13 http://archive.ubuntu.com/ubuntu/ precise-updates/main aptdaemon-data all 0.43+bzr805-0ubuntu9 [163 kB] 

Get:14 http://archive.ubuntu.com/ubuntu/ precise-updates/main python-aptdaemon.g tk3widgets all 0.43+bzr805-0ubuntu9 [15.0 kB] 

Get:15 http://archive.ubuntu.com/ubuntu/ precise/universe synaptic i386 0.75.9ub untu1 [2,405 kB] 

Get:16 http://archive.ubuntu.com/ubuntu/ precise-updates/main aptdaemon all 0.43 +bzr805-0ubuntu9 [16.0 kB] 

Err http://archive.ubuntu.com/ubuntu/ precise-updates/main python-software-prope rties all 0.82.7.3 404 Not Found [IP: 91.189.88.149 80] 

Err http://archive.ubuntu.com/ubuntu/ precise-updates/main software-properties-c ommon all 0.82.7.3 404 Not Found [IP: 91.189.88.149 80] 

Err http://archive.ubuntu.com/ubuntu/ precise-updates/main software-properties-g tk all 0.82.7.3 404 Not Found [IP: 91.189.88.149 80] 

Fetched 4,012 kB in 7s (558 kB/s) Failed to fetch http://archive.ubuntu.com/ubuntu/pool/main/s/software-properties /python-software-properties_0.82.7.3_all.deb 404 Not Found [IP: 91.189.88.149 80] 

Failed to fetch http://archive.ubuntu.com/ubuntu/pool/main/s/software-properties /software-properties-common_0.82.7.3_all.deb 404 Not Found [IP: 91.189.88.149 80] 

Failed to fetch http://archive.ubuntu.com/ubuntu/pool/main/s/software-properties /software-properties-gtk_0.82.7.3_all.deb 404 Not Found [IP: 91.189.88.149 80] 

E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?