Comment 68 for bug 153980

I am getting the same error when trying to upgrade from 7.04 to 7.10

The problem seems to be that something in update manager is replacing the file:
/etc/apt/sources.list.d/prerequists-sources.list
(no typo - that is the filename...)
with one that has hardcoded the us.archive.ubuntu.com repo.
and us.archive.ubuntu.com has no longer the 7.04 feisty packages

I have already replaced all in /etc/apt/sources.list with old-releases.ubuntu.com
I even replaced the entry in /etc/apt/sources.list.d/prerequists-sources.list, but update manager replaces that whole file.