Sorry, it's still not clear from the previous conversation -- in addition to updating to Centos 6.6, have you also switched to the official Xen4CentOS repos (i.e., by installing centos-release-xen)?
Sorry for not making it clear! :)
Yes, I upgraded to both CentOS 6.6 and Xen4CentOS, although because we're building packages in a mock we're using the repository (http://mirror.centos.org/centos/6/xen4/x86_64/) directly for both the build and the install.
Bob