When you host a Centos 6 Xen VM on a CentOS 5 node, you will need to fix the disk name in order for vm to boot.
disk = ['phy:/dev/VolGroup00/vm281_img,sda1,w', 'phy:/dev/VolGroup00/vm281_swap,sda2,w']
to:
disk = ['phy:/dev/VolGroup00/vm281_img,xvda1,w', 'phy:/dev/VolGroup00/vm281_swap,xvda2,w']
I have to lock the file using chattr +i vmX.config and to modify the file again manually you need to undo by chattr -i
