"WARNING:root:file 'saucy.tar.gz.gpg' missing" on distribution upgrade

Question

I'm trying to upgrade from 13.04 to 13.10 following this guide: http://www.unixmen.com/upgrade-ubuntu-13-04-raring-ubuntu-13-10-saucy-salamander/

user@computer:~ update-manager
Fontconfig warning: "/etc/fonts/conf.d/50-user.conf", line 9: reading configurations from ~/.fonts.conf is deprecated.
Fontconfig warning: "/etc/fonts/conf.d/50-user.conf", line 9: reading configurations from ~/.fonts.conf is deprecated.
gpg: /tmp/tmp82g1kk/trustdb.gpg: trustdb created
Checking for a new Ubuntu release
WARNING:root:file 'saucy.tar.gz.gpg' missing
Traceback (most recent call last):
  File "/usr/bin/do-release-upgrade", line 152, in <module>
    fetcher.run()
  File "/usr/lib/python3/dist-packages/DistUpgrade/DistUpgradeFetcherCore.py", line 278, in run
    _("Fetching the upgrade failed. There may be a network "
  File "/usr/lib/python3/dist-packages/DistUpgrade/DistUpgradeFetcher.py", line 50, in error
    return error(self.window_main.window_main, summary, message)
AttributeError: 'NoneType' object has no attribute 'window_main'

Answer 1

I had apt-cacher installed.

https://help.ubuntu.com/community/Apt-Cacher-Server

Remove or edit the proxy file you added in /etc/apt/apt.conf.d/ to bypass apt-cacher.

Answer 2

I was getting "Failed to fetch" too. Changing the software sources in "Software & Updates" back to the "Main server" servers instead of the country specific "Server for country" let the upgrade continue.