There are some packages missing but nothing too serious.
This problem usually occurs when there is a bad cached copy or the repository is being updated.

Not much you can do. It should go away on its own. If you still want to try something try:

rm -R /var/lib/apt/lists/repository.maemo.org_extras*
apt-get autoclean

Then go to: (geneven's link) http://nokiadistrict.com/repositorie...or-nokia-n900/
and readd the repositories.

Edit: It is more sensible to try with a differenet Wi-Fi connection. Preferibly from a different ISP.