The virtual server fails to start with the following message:
Running: create_domain_xml LibVirt: Call to virDomainCreateXML failed: XML error: invalid maximum number of vCPUs '0'
KVM compute resources
service libvirtd restart on the compute resource where the virtual server failed to start. If it does not fix the issue, you can cold migrate the virtual server to another compute resource and start it there.
Libvirtd may have started with incorrect parameters or there are too many virtual servers currently running on the compute resource.