problem with emerge after rsync and update system

After doing an 'emerge rsync' and 'emerge -u system', updating world doesn't 
work any more. The updated packages included python, perl and portage.
A friend of mine is getting the same error and a new rsync doesn't help.
Here is what I get from the console:

root@matrix portage # emerge -p -u world

These are the packages that I would merge, in order.

Calculating world dependencies |
!!! Error: couldn't find match for virtual/opengl in kde-base/kdeartwork-3.0.1