Apologies for the very late reply. An educated guess would be a proxy configuration issue is blocking the web-calls the VIM SDK uses to connect to the VM host server. Were you able to determine the root cause?
Thanks for the reply, It turns out there was a back end Firewall change (ports) put though without notice which blocked the communications.
Once this was resolved and allowed though, then this feature came back on.
This customer have a highly firewalled environment, one of the tightest ive seen. So was a new challenge.