When opening the EMC or EMS on an Exchange 2010 server, you may encounter this error:

Error

The attempt to connect to http://server.domain.local/Powershell user 'Kerberos' authentication failed: Connecting to remote server failed with the following error message: The WS-Management service cannot process the request. The system 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.

To workaround the issue, perform a restart of IIS: open an elevated command prompt and run:

iisreset /restart

After the restart, you will be able to log in again. Note that restarting IIS will briefly disrupt service to the end-users.