Upgrade to F11, now yum python module missing

[Stefan Grosse]

During the DVD upgrade from F10 -> F11 I encountered the issue that my
yum appears broken now:


"There was a problem importing one of the Python modules
required to run yum. The error leading to this problem was:

   No module named yum

Please install a package which provides this module, or
verify that the module is installed correctly.

It's possible that the above module doesn't match the
current version of Python, which is:
2.6 (r26:66714, Mar 17 2009, 11:44:21) 
[GCC 4.4.0 20090313 (Red Hat 4.4.0-0.26)]

If you cannot solve this problem yourself, please go to 
the yum faq at:
  http://wiki.linux.duke.edu/YumFaq"

Could someone please give me a quick pointer how to get yum running?

Thanks
Stefan

btw. I also had the problem that I could not even start the upgraded
system because I had the proprietory nvidia driver initially which was
obviosly neither upgraded nor deactivated. I could not even get to any
kind of console so that I had to use systemrescuecd to edit xorg.conf
and activate the nv driver (nouveau does not work either)