Comment 2 for bug 235527

I'm confronting this bug now, which is particularly frustrating because the notice on old-releases.ubuntu.com specifically says:

(Ubuntu 6.10 is still supported, but is distributed from this site for space reasons.)

But I wanted to clarify the procedure. When do-release-upgrade complains about mirrors, you must edit sources.list while the [yN] question is being asked. So suspend your d-release-upgrade process with control-Z or open another terminal window and edit your sources.list. Then back in the running do-release-upgrade process, say "Y" and you'll have slipped the new sources.list into the mix without it ever being wiser.

but what a hassle!