I ran "do-release-upgrade -d" on an Ubuntu 10.10 (Maverick) box, but the 
command failed while trying to download natty.tar.gz, which would be 
Ubuntu 11.04:

Checking for a new ubuntu release
Err Upgrade tool signature
    404  Not Found [IP: 91.189.91.14 80]
Err Upgrade tool
    404  Not Found [IP: 91.189.91.14 80]
Fetched 0B in 0s (0B/s)
WARNING:root:file 'natty.tar.gz.gpg' missing
Failed to fetch
Fetching the upgrade failed. There may be a network problem.


There is no network problem, at least not on my end.  So what do you think 
I can do about that?  It's not that big of a deal to just start from 
scratch, but this is annoying.  I don't know where it is getting that IP, 
but it seems to be the wrong IP.

Is there another way to do the upgrade?

If I have a new ISO, can I just use that to upgrade to the latest version?

TIA,
Mike