This is an old question here, but I still want to make an update for my solution:

It could also be a problem with uncompatible packages, I upgraded several packages in my Ubuntu, then this problem was fixed:

ii libvirt-bin 1.2.12-0ubuntu14.2~cloud0 amd64 programs for the libvirt library

ii libvirt0 1.2.12-0ubuntu14.2~cloud0 amd64 library for interfacing with different virtualization systems

ii libxen-4.4 4.4.2-0ubuntu0.14.04.2 amd64 Public libs for Xen

And the error sometimes reported as this:

2015-11-06 15:24:28.844 3411 TRACE nova.compute.manager [instance: 94cf1f3d-b3bc-4fdc-9462-5fa3cd1335b0] if ret == -1: raise libvirtError ('virDomainCreateWithFlags() failed', dom=self) 2015-11-06 15:24:28.844 3411 TRACE nova.compute.manager [instance: 94cf1f3d-b3bc-4fdc-9462-5fa3cd1335b0] libvirtError: invalid argument: monitor must not be NULL

Thanks.

Check this : - https://answers.launchpad.net/nova/+q...
and this https://ask.openstack.org/en/question...