Comment 2 for bug 109397

I found the error. It appeared to be Firestarter that was blocking the connection to archive.ubuntu.com when "Block traffic from reserved addresses on public interfaces" was set (which seems like a bug to me - it doesn't happen in Feisty though). I tried several times so set and unset that setting and it was clearly related to being able to connect to the ubuntu server or not.

When I had found that out and unmarked that setting in Firestarter, update-manager was able to download the ReleaseAnnouncements file and the upgrade could start.