cobbler system powerstatus returns "Could not determine MAC [ ]"

I followed pretty much everything detailed in the following blog and linked part1 and part2 post:

http://cloud.ubuntu.com/2011/10/ubuntu-cloud-deployment-with-orchestra-and-juju/

After getting the ubuntu-orchestra-server working, I was able to have servers to PEX-boot from it, but the following command line returns MAC address not determined:

sudo cobbler system powerstatus --name oneiric02.ubuntu.lan

The systems are set as oneiric-i386-juju profile. I tried poweron poweroff, all got the same result. Is there any suggestion to get the Orchestra power management to work?

Thanks in advance!

Stephan