Maybe you have just a wrong url. Go to http://www.gutenberg.org/ebooks/ first to see if the error persists.
If you get the error again check that you:
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Don't access Project Gutenberg from hosted servers.
Don't use automated software to download lots of books. We have a limit on how fast you can go while using this site. If you surpass this limit you get blocked for 24h.
We have a daily limit on how many books you can download. If you exceeded this limit you get blocked for 24h.
If you use the RSS feed, set your update interval to 24 hours.
If you are sure that none of the above applies to you,
and wish us to investigate the problem,
we need to know your IP address.
don't sign up,
just copy the IP address
(it looks like: 12.34.56.78 but your numbers will be different)
If that page also shows a proxy address, we need that one too.}