Today I was trying to run do-release-upgrade to upgrade an old 10.04 LTS Ubuntu server, but the upgrade kept failing. It turns out the old release had problems verifying new packages.
The log files for the upgrade process are located in /var/log/dist-upgrade/, with the main file being main.log. The log file indicated that there was an Error authenticating some packages, most likely do to the age of the current release, as seen in this bug report.
I found a fix at http://sysadm.mielnet.pl/upgrading-ubuntu-10-04-to-12-04-error-authenticating-some-packages/:
Create a file /etc/update-manager/release-upgrades.d/unauth.cfg with the contents:
[Distro]
AllowUnauthenticated=yesThis will tell the upgrade process to ignore package authentication error. Don’t forget to remove unath.cfg after the upgrade!
Nicholas Sideras 