Comment 1 for bug 1157272

Uninstalling vbox solved the problem...

Pretty weird, I don't run any vbox vm anymore...

I couldn't simply uninstall vbox 4.1 (yeah, I was out of date since 4.2 is the new stable for months), there were two processes from vbox still running (probably started at boot). I had to kill them first and then 'sudo service libvirt-bin restart' to successfully create the vm.