You are working in a native Microsoft Exchange Server 2010 environment or in a mixed Exchange Server 2010 and Microsoft Exchange Server 2007 environment.
You cannot manage the following virtual directories from Exchange Management Console (EMC):
Outlook Web Access (OWA)
Exchange Control Panel (ECP)
When you expand the server configuration list in EMC, you see a list of CAS servers on the right side.
You try to select an Exchange Server 2007 Client Access Server (CAS) server or an Exchange Server 2010 CAS server.
When you try to select one of the CAS servers, you discover that it is inaccessible.
In this scenario, you receive an error message that resembles the following:
The task wasn't able to connect to IIS on the server <CAS server name>. Make sure that the server exists and can be reached from this computer. The RPC server is unavailable. It was running the command 'Get-OwaVirtualDirectory'.
When you try to select the Client Access server in EMC, the Exchange Server 2010 server runs a Get-OwaVirtualDirectory command in the Exchange Server background. However, you cannot manage any of the virtual directories for the Exchange Server CAS servers if the command cannot access any one of the Exchange Server CAS servers.
To work around this issue, wait until the Exchange Server CAS server that is not responding comes back on line or, use Exchange Management Shell to manage the virtual directories explicitly.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.