PowerCLI is a very flexible tool for vSphere automation. One morning, I connect to vSphere environment & found this error. See Fig-1.
"The underlying connection was closed: An unexpected error occurred on a send"
Fig-1: Error connecting to vCenter
I can ping to vCenter server & can connect to vSphere Web Client. So, I checked for the $Error[0] for exception, it is likely to be a certificate error. But, when I checked the certificate by vSphere Web Client, it's not going to be expired soon.