This problem still exists because the problem is with the configuration of Ubuntu's
servers (such as "archive.ubuntu.com"), not the distribution it produces. To summarize,
Ubuntu's archive servers return wrong headers for gpg files, and this causes errors
when there is a proxy between the computer running Ubuntu's upgrade program and
Ubuntu's archive servers.
I encountered the same problem when I tried to upgrade from 6.06 to 8.04 a few
days ago. When I disabled the proxy configuration for apt by modifying apt's
configuration, the upgrade worked. This is expected, as can be understood from
the description of the bug.
I would appreciate it if the configuration of Ubuntu's archive servers could be fixed.
Please read the description of this bug to learn about the problem in the configuration
of Ubuntu's archive servers. (I did not actually let the upgrade begin, so I can still test
the server if the configuration of the server is eventually changed.)
M. Vefa Bicakci