Just out of curiosity why are you trying to upgrade to 12.10? Ubuntu 12.10 is coming to an EOL which means End Of Life and it's gonna be during April 2014.
My advice to wait for other LTS to be released that is 14.04 LTS Trusty Tahr which is scheduled to be released in April 2014. Then you can upgrade your current LTS release to a new LTS release what is Trusty Tahr.
To upgrade current release run
sudo do-release-upgrade or insert your Ubuntu LiveCD and choose upgrade to the next LTS release.
more tutorial for LTS releases:
- Start System/Administration/Software Sources
- On the Updates tab, set Show new distribution releases: to Long term support releases only, then press Close.
- Press Alt-F2 and type
- Click the Check button to check for new updates. If there are any updates to install, use the Install Updates button to install them, and press Check again after that is complete.
- A message will appear informing you of the availability of the new release. Click Upgrade.
Follow the on-screen instructions.
Also if you'd like to be notified about new LTS release run:
sudo gedit /etc/apt/sources.list
Updates tab and at the bottom make sure is set to
notify me about new LTS release and you'll be notified when it's released.