Upgrade to 7.10 stops

1) I tried to upgrade 7.04 to 7.10 over the network, through the update manager, several times. The upgrade always stops in the second step (Modifying the software channels), with a message Fetching file 51 of 69. Nothing happens for quite a while, no network activity, no hard disk activity (I let it try for about an hour). After cancelling, the eror message said:

Failed to fetch http://archive.ubuntu.com/ubuntu/dists/gutsy/Release.gpg
Failed to fetch http://archive.ubuntu.com/ubuntu/dists/gutsy/main/i18n/Translation-en_US.bz2
Failed to fetch http://archive.ubuntu.com/ubuntu/dists/gutsy/restricted/i18n/Translation-en_US.bz2
Failed to fetch http://archive.ubuntu.com/ubuntu/dists/gutsy/universe/i18n/Translation-en_US.bz2
Failed to fetch http://archive.ubuntu.com/ubuntu/dists/gutsy/multiverse/i18n/Translation-en_US.bz2
Failed to fetch http://archive.ubuntu.com/ubuntu/dists/gutsy/multiverse/i18n/Translation-en_US.bz2
Failed to fetch http://archive.ubuntu.com/ubuntu/dists/gutsy/universe/i18n/Translation-en_US.bz2
Failed to fetch http://archive.ubuntu.com/ubuntu/dists/gutsy-updates/Release.gpg
Failed to fetch http://archive.ubuntu.com/ubuntu/dists/gutsy-updates/main/i18n/Translation-en_US.bz2
Failed to fetch http://archive.ubuntu.com/ubuntu/dists/gutsy-updates/restricted/i18n/Translation-en_US.bz2
Failed to fetch http://archive.ubuntu.com/ubuntu/dists/gutsy-updates/universe/i18n/Translation-en_US.bz2
Failed to fetch http://archive.ubuntu.com/ubuntu/dists/gutsy-updates/multiverse/i18n/Translation-en_US.bz2
Failed to fetch http://archive.ubuntu.com/ubuntu/dists/gutsy-updates/multiverse/i18n/Translation-en_US.bz2
Failed to fetch http://archive.ubuntu.com/ubuntu/dists/gutsy-updates/universe/i18n/Translation-en_US.bz2
Failed to fetch http://security.ubuntu.com/ubuntu/dists/gutsy-security/Release.gpg
Failed to fetch http://security.ubuntu.com/ubuntu/dists/gutsy-security/main/i18n/Translation-en_US.bz2
Failed to fetch http://security.ubuntu.com/ubuntu/dists/gutsy-security/restricted/i18n/Translation-en_US.bz2
Failed to fetch http://security.ubuntu.com/ubuntu/dists/gutsy-security/multiverse/i18n/Translation-en_US.bz2
Failed to fetch http://security.ubuntu.com/ubuntu/dists/gutsy-security/universe/i18n/Translation-en_US.bz2
Failed to fetch http://archive.canonical.com/ubuntu/dists/gutsy/Release.gpg
Failed to fetch http://archive.canonical.com/ubuntu/dists/gutsy/partner/i18n/Translation-en_US.bz2
Failed to fetch http://archive.ubuntu.com/ubuntu/dists/gutsy-backports/Release.gpg
Failed to fetch http://archive.ubuntu.com/ubuntu/dists/gutsy-backports/main/i18n/Translation-en_US.bz2
Failed to fetch http://archive.ubuntu.com/ubuntu/dists/gutsy-backports/restricted/i18n/Translation-en_US.bz2
Failed to fetch http://archive.ubuntu.com/ubuntu/dists/gutsy-backports/universe/i18n/Translation-en_US.bz2
Failed to fetch http://archive.ubuntu.com/ubuntu/dists/gutsy-backports/multiverse/i18n/Translation-en_US.bz2
Failed to fetch http://archive.ubuntu.com/ubuntu/dists/gutsy-security/Release.gpg
Failed to fetch http://archive.ubuntu.com/ubuntu/dists/gutsy-security/main/i18n/Translation-en_US.bz2
Failed to fetch http://archive.ubuntu.com/ubuntu/dists/gutsy-security/restricted/i18n/Translation-en_US.bz2
Failed to fetch http://archive.ubuntu.com/ubuntu/dists/gutsy-security/universe/i18n/Translation-en_US.bz2
Failed to fetch http://archive.ubuntu.com/ubuntu/dists/gutsy-security/multiverse/i18n/Translation-en_US.bz2

2) I tried to upgrade using the alternate CD, but the upgrade also stops in the second step, saying that it was not possible to verify the following files:

alsa-oss
amarok
amarok-xine
arj
aspell-es
autotools-dev
beagle
binfmt-support
ca-certificates
cdda2wav
cdrecord
checkinstall
clamav-docs
dictzip
dosbox
dselect
dvdauthor
dvdrip
esound
faad
feisty-wallpapers
festival
ffmpeg
fftw3
firestarter
foomatic-gui
g-wrap
gaim
gawk
gcj-4.1-base
gdk-imlib11
gdk-imlib11-dev
gij-4.1
gimp-help-common
gimp-help-cs
gimp-help-de
gnome-alsamixer
gnome-bin
gnome-commander
gnome-libs-data
gnomebaker
gnucash
gnucash-common
gnucash-docs
gramps
grip
gs-common
gs-esp
gs-esp-x
gstreamer0.10-ffmpeg
gstreamer0.10-fluendo-mp3
gstreamer0.10-fluendo-mpegdemux
gstreamer0.10-gl
gstreamer0.10-gnonlin
gstreamer0.10-pitfdll
gstreamer0.10-plugins-bad
gstreamer0.10-plugins-bad-multiverse
gstreamer0.10-plugins-ugly
gstreamer0.10-plugins-ugly-multiverse
gstreamer0.10-sdl
guile-1.6
guile-1.6-dev
guile-1.6-slib
guile-g-wrap
gutenprint-doc
gwget
icedax
imagemagick
imlib-base
indent
ingerman
iogerman
ispell
java-common
k3b
kdebase-bin
kdebase-kio-plugins
kdelibs-data
kdelibs4c2a
kdesktop
khelpcenter
kmymoney2
lame
language-pack-kde-cs
language-pack-kde-cs-base
language-pack-kde-de
language-pack-kde-de-base
language-pack-kde-en
language-pack-kde-en-base
language-pack-kde-es
language-pack-kde-es-base
lha
liba52-0.7.4
libaqbanking-data
libaqbanking-plugins-libgwenhywfar38
libaqbanking16
libaqdtaus3
libaqgeldkarte4
libaqhbci10
libarchive-tar-perl
libarchive-zip-perl
libarchive1
libart-2.0-dev
libart-dev
libart2
libarts1c2a
libartsc0
libatk1.0-dev
libaudio2
libavahi-client-dev
libavahi-common-dev
libavahi-glib-dev
libavahi-qt3-1
libavcodec1d
libavformat1d
libavutil1d
libbonobo2-dev
libbonoboui2-dev
libbtctl4
libcairo-java
libcairo-jni
libcairo2-dev
libcarp-clan-perl
libcdaudio1
libclamav2
libcompress-raw-zlib-perl
libcompress-zlib-perl
libcrypt-ssleay-perl
libcurl3
libdb3
libdb4.3
libdbus-1-dev
libdbus-glib-1-dev
libdc1394-13
libdvdnav4
libdvdread3
libesd0-dev
libestools1.2
libevent-execflow-perl
libexpat1-dev
libfaad2-0
libffi4
libffi4-dev
libfinance-quote-perl
libflac++6
libfontconfig1-dev
libfreebob0
libfreetype6-dev
libgail-dev
libgcj7-1
libgconf2-dev
libgcrypt11-dev
libgdiplus
libglade2-dev
libglib-java
libglib-jni
libglib2.0-dev
libgmp3c2
libgnome-keyring-dev
libgnome2-dev
libgnome32
libgnomebt0
libgnomecanvas2-dev
libgnomeprint2.2-dev
libgnomeprintui2.2-dev
libgnomesupport0
libgnomeui-dev
libgnomeui32
libgnomevfs2-dev
libgnorba-dev
libgnorba27
libgnorbagtk0
libgnutls-dev
libgnutlsxx13
libgoffice-0-4
libgoffice-0-common
libgpg-error-dev
libgsf-gnome-1-114
libgsm1
libgtk-jni
libgtk2.0-dev
libgwenhywfar-data
libgwenhywfar38
libgwrap-runtime0
libgwrap-runtime0-dev
libhal-dev
libhal-storage-dev
libhtml-tableextract-perl
libice-dev
libid3-3.8.3c2a
libid3tag0
libidl-dev
libimlib2
libintl-perl
libio-compress-base-perl
libio-compress-zlib-perl
libjack0
libjack0.100.0-0
libjaxp1.2-java
libjpeg62-dev
libk3b2
libk3b2-mp3
libkbanking1
libkonq4
libktoblzcheck1c2a
liblame0
libltdl3-dev
liblzo2-dev
libmad0
libmdbtools
libmjpegtools0c2a
libmms0
libmodplug0c2
libmono-data-tds1.0-cil
libmono-security1.0-cil
libmono-sharpzip0.6-cil
libmono-sharpzip0.84-cil
libmono-sqlite1.0-cil
libmono-system-data1.0-cil
libmono-system-runtime1.0-cil
libmono-system-web1.0-cil
libmono1.0-cil
libmp4v2-0
libmpcdec3
libmysqlclient15off
libncurses5-dev
libntfs-3g-dev
libofa0
libofx3
libopencdk8-dev
libopenexr2c2a
libopenobex1
libopenspc0
liborbit2-dev
libosp5
libpam-smbpass
libpango1.0-dev
libpng12-dev
libpostproc1d
libpvm3
libqbanking4
libqt3-mt
libqt4-core
libqt4-gui
libqt4-qt3support
libqt4-sql
libquicktime1
libreadline5-dev
librsync1
libruby1.8
libsdl-sound1.2
libselinux1-dev
libsepol1-dev
libsm-dev
libsmpeg0
libsqlite0
libstlport5.1
libswfdec0.3
libswscale1d
libswt3.2-gtk-jni
libtasn1-3-dev
libtext-glob-perl
libtool
libtool-doc
libtunepimp5
libungif4g
libuser1
libwrap0-dev
libx11-dev
libx264-54
libxau-dev
libxcb-shape0
libxcb-shm0
libxcb-xv0
libxcb1
libxcomposite-dev
libxcursor-dev
libxdamage-dev
libxdmcp-dev
libxext-dev
libxfixes-dev
libxft-dev
libxi-dev
libxine1
libxine1-ffmpeg
libxinerama-dev
libxml2-dev
libxmlsec1
libxmlsec1-nss
libxmlsec1-openssl
libxrandr-dev
libxrender-dev
libxvidcore4
libxvmc1
mencoder
menu
mjpegtools
mkisofs
mozilla-firefox-locale-cs-cz
mozilla-firefox-locale-de-de
mozilla-firefox-locale-es-ar
mozilla-firefox-locale-es-es
mozilla-mplayer
mozilla-thunderbird
mplayer
mplayer-skins
msttcorefonts
myspell-cs-cz
myspell-de-at
myspell-de-ch
myspell-de-de
myspell-es
mysql-common
ntp
odbcinst1debian1
openoffice.org-filter-mobiledev
openoffice.org-help-cs
openoffice.org-help-de
openoffice.org-help-en-gb
openoffice.org-help-es
openoffice.org-hyphenation-de
openoffice.org-l10n-cs
openoffice.org-l10n-de
openoffice.org-l10n-es
openoffice.org-style-andromeda
openoffice.org-style-default
openoffice.org-style-industrial
openoffice.org-thesaurus-cs
openoffice.org-thesaurus-de
openoffice.org-thesaurus-de-ch
p7zip
p7zip-full
pdmenu
pmount
psfontmgr
python-crypto
python-foomatic
python-qt3
python-sip4
python2.4
python2.4-minimal
revelation
ruby1.8
samba-doc
sbackup
sharutils
smbfs
soundconverter
sox
stardict
stardict-common
sun-java5-bin
sun-java5-jre
sun-java6-bin
sun-java6-jre
sun-java6-plugin
tango-icon-theme
tcl8.4
thunderbird
thunderbird-locale-cs
thunderbird-locale-de
thunderbird-locale-es-ar
thunderbird-locale-es-es
tk8.4
totem-xine
transcode
ttf-arphic-ukai
ttf-bengali-fonts
ttf-dejavu
ttf-dejavu-extra
ttf-devanagari-fonts
ttf-gujarati-fonts
ttf-indic-fonts
ttf-kannada-fonts
ttf-oriya-fonts
ttf-punjabi-fonts
ttf-tamil-fonts
ttf-telugu-fonts
tzdata
unace
unixodbc
unrar
unzoo
vnc-common
vorbis-tools
winbind
wine
wngerman
wogerman
wswiss
x-dev
x11proto-composite-dev
x11proto-core-dev
x11proto-damage-dev
x11proto-fixes-dev
x11proto-input-dev
x11proto-randr-dev
xkeyboard-config
xtrans-dev
xvncviewer
zlib1g-dev

I don't know how to proceed. Any ideas what might be wrong?