failed to fetch

[Pietro Bergamo]

I've been trying to update from feisty to gutsy (by simply clicking the button in the update manager), but the update manager always stops giving me an error message, "failing to fetch" these three files:

Failed to fetch http://archive.ubuntustudio.org/ubuntustudio/dists/feisty/Release.gpg Não foi possível resolver 'archive.ubuntustudio.org'
Failed to fetch http://archive.ubuntustudio.org/ubuntustudio/dists/feisty/main/i18n/Translation-pt_BR.bz2 Não foi possível resolver 'archive.ubuntustudio.org'
Failed to fetch http://archive.ubuntustudio.org/ubuntustudio/dists/feisty/main/binary-i386/Packages.gz Não foi possível resolver 'archive.ubuntustudio.org'

Does anybody know what's wrong? Sorry if I'm doing something stupid.

Thanks, 
Pietro




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