RESOLVED: The WS-Management service cannot process the request. The user load quota of 1000 requests per 2 seconds has been exceeded. Send future requests at a slower rate or raise the quota for this user. The next request from this user will not be approved for at least X milliseconds.
This can happen if your Exchange server has recently received a new SSL (UCC) certificate.
What can happen is the remote PowerShell or the EMC will be using a certificate that is not trusted or valid anymore.
A simple "IISRESET" from PowerShell or the CMD prompt will correct the issue.