Your problem can be the fact of server is offline and the packages cant be down.
Or you have a corrupt sources.list.
For the first , maybe in one or two days the server is up and then you can connect to him.
For the second as ardvark71 comment maybe can help if you can put the content of sources.list to our users see if have a problem on it. If your sources.list is wrong you can request a sources.list of other user of debian with the same arquitecture and the same version, or use a site like ->
http://debgen.simplylinux.ch/
The problem is on your connection to the target so isnt a big problem.