"An upgrade from 'precise' to 'oneiric' is not unsupported with this tool" error while upgrading

A brief electrical outage interrupted my 12.04 upgrade. After many tries, which included trying to upgrade from a command line, I was able to access Ubuntu screens again.

I find that the 12.04 upgrade was indeed not completed; I am still running 11.10. However, Update Manager does not give me the option of installing 12.04 now.

And, when I run Update Manager, I am asked if I want to execute a "partial install." When I answer "yes," I receive the message above. Besides a clean install, any ideas about what can I do to upgrade to 12.04?

Try running sudo apt-get dist-upgrade.

It means your upgrade crashed during the failed system upgrade.

Try this:

1. Press Ctrl+Alt+T to open a Terminal window.

2. Run these commands:

   sudo rm -rf /var/lib/apt/lists/*
   sudo apt-get update
   

   That might be sufficient to fix the problem. If not, continue on...

3. Run the command

   gksu gedit /etc/*release
   

   and change everything in the file gedit brings up to:

   DISTRIB_ID=Ubuntu
   DISTRIB_RELEASE=11.10
   DISTRIB_CODENAME=Oneric
   DISTRIB_DESCRIPTION="Ubuntu 11.10"
   

   Save the file.

4. Then run this command.:

   gksu gedit /etc/*issue
   

   And change the file to to:

   Ubuntu 11.10 \n \l
   

Now open the Update Manager and upgrade the OS as usual.