error when upgrading

[CascadeX]

I get the following message when trying to upgrade from 10.10 to 11.04

W:Failed to fetch http://extras.ubuntu.com/ubuntu/dists/natty/Release.gpg Something wicked happened resolving 'extras.ubuntu.com:http' (-5 - No address associated with hostname)
, E:Some index files failed to download, they have been ignored, or old ones used instead.

[dino99]

you might check again, it works here

[aerofly5]

check your internet connection? Try pinging the address if your connected and still having troubles