I have spent the last week or so, exporting VMs from a Xen 6 Server to a Hyper-V server.
All was going well, until I hit the last one. One of the Domain controllers.
As with every other server, I had shut down the server, opened the Xen Center console, right clicked and selected Export.
Except this time, it failed.
It took a few minutes to figure out, but the reason this failed to export, was because the server I had just powered off, was also the local DHCP server.
It turns out, that the Xen server spins up a hidden VM to do the export. During this spin up, it needs an IP address - which it couldnt get - and therefore failed to export the server.
Thankfully I had also installed the DHCP role on another server, so not too much time was lost.