"The cluster cannot be configured with the selected Enhanced vMotion Compatibility mode; CPU features disabled by that mode may currently be in use by powered-on or suspended virtual machines in the cluster."
In order to enable EVC you will have to shutdown the VM which is using the CPU features. In your case it is vCenter. Shutdown vCenter and cold migrate it to new server and power it ON. But do check this KB for vMotion compatibility.
http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=100321...
Give me processor name I can confirm if you need to?
Thank you
With Great Regards,
