Its likely that it failed to connect to the automation socket. VIX needs to talk to port 902 on the ESX system in order to execute guest operations, and it tries to get that connection when poweringOn. Be sure there's no firewalls in place.
We also recently found a bug where there was some case-sensitivity in the URL used for the connection. 'https://<ip>/sdk' worked fine, but 'Https://<ip>/sdk' did not, because some code couldn't handle the upper case.