packages size mismatch in archives

[Ing. Vladimir M. Kerka]

Hi,
I'm quite new in Ubuntu and I'm trying to install Ubuntu on AMD 64, but 
there are LOTS of packages in the archives with the size mismatch:
Failed to fetch 
http://archive.ubuntu.com/ubuntu/pool/main/d/docbook-xml/docbook
-xml_4.3-1.1_all.deb  Size mismatch
Failed to fetch 
http://archive.ubuntu.com/ubuntu/pool/universe/g/glade/glade-com
mon_0.6.4-13.1_all.deb  Size mismatch
Failed to fetch 
http://archive.ubuntu.com/ubuntu/pool/main/g/gnome-doc-tools/gno
me-doc-tools_1.0-6.1_all.deb  Size mismatch
Failed to fetch 
http://archive.ubuntu.com/ubuntu/pool/universe/g/gnome-tasksel/g
nome-tasksel_0.9.7.1_all.deb  Size mismatch
Failed to fetch 
http://archive.ubuntu.com/ubuntu/pool/universe/libg/libgda/libgd
a-dev_0.2.96-6_amd64.deb  Size mismatch
Failed to fetch 
http://archive.ubuntu.com/ubuntu/pool/universe/g/gnome-vfs/libgn
ome-vfs-dev_1.0.5-5_amd64.deb  Size mismatch
Failed to fetch 
http://archive.ubuntu.com/ubuntu/pool/universe/g/gnome-db/libgno
medb-dev_0.2.96-9_amd64.deb  Size mismatch

I may give you at least 10 another examples for glade, bonobo, gsf etc.

This sitauation prevents me from installing such essential packages, 
like gnome-panel, gnome-session, nautilus, scrollkeeper, synaptic.

What am I supposed to do?

Thanks for your help

Vlada
-- 
Ing. Vladimir M. Kerka
Klukovicka 1530
155 00 Praha 5 - Stodulky
Czech Republic
e-mail: kerka at dinmont.cz
         kerka at chello.cz
web:    www.dinmont.cz

NOTE: rm -rf /bin/ladin
Nedostavam a nerozesilam viry, protoze nepouzivam M$ Windows