Sometimes when upgrading Ubuntu you'll see this error message:
Error authenticating some packages It was not possible to authenticate some packages. This may be a transient network problem. You may want to try again later. See below for a list of unauthenticated packages
Temporary workaround, create file
/etc/update-manager/release-upgrades.d/unauth.cfg
filled with the following
[Distro] AllowUnauthenticated=yes
Now your sudo do-release-upgrade should run OK.
Make sure to remove this file once upgrade process is completed.
Source: http://sysadm.mielnet.pl/upgrading-ubuntu-10-04-to-12-04-error-authenticating-some-packages/