I was able to connect my PowerCLI instance without any problems to my vCenter, until all of a sudden I got the following error:
Connect-VIServer : 8/12/2010 11:51:36 Connect-VIServer
Could not connect using the requested protocol.
I discovered that this was due to a change in the Proxy Server settings on the client. After removing this proxy address everything was back to normal.
-ray
You can also use the Set-PowerCLIConfiguration cmdlet with the -ProxyPolicy NoProxy parameter to turn it off for that PowerCLI session.
Thanks for the tip,
I got the same problem today.