Comment 7 for bug 848659

I am now confused:
- my 64-bit server upgraded from a CD burnt from the 20110915 daily 64-bit server ISO, with no problems
- upgrade of a 64-bit VM which has no additional software succeeds using the 64-bit alternate ISO 20110920.5
- attempts to upgrade my main PC, running 64-bit natty, fail with the same error, during step 2 (setting new channels), using a CDRW created from any of:
  * 20110915 64-bit alternate ISO
  * 20110915 64-bit server ISO
   20110920.5 64-bit alternate ISO

In addition, do-release-upgrade can't find a development release, so I can't even use that to upgrade:
tim@zaphod:~$ sudo do-release-upgrade -d
[sudo] password for tim:
Checking for a new ubuntu release
No new release found
tim@zaphod:~$

The attempts to upgrade my main system DID fetch packages files from an acceptable repository even if I chose "NO" at the "Fetch latest updates from the network" question. It appears that the question only affects packages that are available from the CD - the packages fetched were from universe or multiverse or from the partner repository http://archive.canonical.com/ubuntu. If that is the case, then the message is misleading.

There is a (or at least a potential) secondary bug, because the upgrade process didn't recognise ucmirror.canterbury.ac.nz as a valid mirror, although natty synaptic offers that as a choice. I suspect that the upgrader doesn't recognise anything other than "*.archive.ubuntu.com" as a valid mirror. I discovered this when I switched mirror after discovering that the Citylink mirror that is considered official (nz.archive.ubuntu.com => ubuntu.citylink.co.nz) was not up-to-date, and tried to do the release update after selecting ucmirror.canterbury.ac.nz. With ucmirror.canterbury.ac.nz, I got 'no valid mirrors found'