I'm glad to see I'm not the only one with this problem.
Correct me if I am wrong but I THINK it is at download.linuxmce.org.
Have you tried
sudo apt-get install --fix-missing
sudo dpkg --configure -a
If you can get into desktop/linuxmce admin page... I recommend looking at your network/settings and make sure that your nics arent swapped.
Those didn't seem to do anything, but I have made a bit of progress and can now at least access the web admin page.
/etc/network/interfaces listed my internal network card as eth0:1 instead of eth1 (missed that when I was first looking at it) so I changed that.
As per the wiki http://wiki.linuxmce.com/index.php/Single_to_Double_NIC
my /etc/default/dhcp3-server contained my external network
instead of my internal network
After rebooting I now have a black screen with a cursor, and several messages appear indicating that avwizard and orbiter was installed, but avwizard still doesn't start (at least I don't think it does). I've read some of the other 'black screen' posts on the forums, but haven't heard any of the beeps, and F7 doesn't do anything. My problem seems very similar to http://forum.linuxmce.org/index.php?topic=9152.msg62799#msg62799
Anyway, I'm going play with the webadmin and see if I can get a little further with this. I'll post an update if I make any progress.