If oz was built from the Git repository, as described in the installation guides, then apt-get update (on Ubuntu) of yum update (CentOS) will fail due to dependency problems while updating the Python packages for OS.
This is because the package (for oz) built locally also needs to be updated to match the Python version. The solution is to remove the package, and then install it again after doing a system update:
sudo yum remove oz sudo yum update # rebuild OZ as detailed in the getting started guide cd ~/git/oz/ git pull rm -f ~/rpmbuild/RPMS/noarch/oz-* make rpm sudo yum localinstall ~/rpmbuild/RPMS/noarch/oz-*.rpm