There are problems when accessing a cluster, the error in the log informs:
(null) (null) Error 1722 The RPC server is unavailable.
Environment: CCR on a Windows 2008 cluster, QMM is installed on XP SP2 (or Server 2003).
When troubleshooting and using the Cluster Administrator from Admin Tools and trying to connect to the same cluster it fails with the same error.
However cluster is fully functional and all nodes are available and online.
Microsoft released a KB article with explanation: http://support.microsoft.com/default.aspx/kb/947299
Error message when you call the OpenCluster function against a Windows Server 2008 cluster from Windows XP or from Windows Server 2003: "The RPC Server is unavailable"
On a computer that is running Windows XP or Windows Server 2003, you call the OpenCluster function against a Windows Server 2008 cluster on a remote server. In this case, you experience a delay of one minute. Then, you receive the following error message:
0x800706ba (The RPC Server is unavailable).
This behavior occurs in Windows XP and in Windows Server 2003 because remote procedure calls (RPC) use User Datagram Protocol (UDP) ports to contact the Cluster service on a remote server.
Windows Server 2008 no longer supports UDP ports in RPC communication. Computers that are running Windows Server 2008 and Windows Vista cannot call the OpenCluster function against a cluster that is running Windows Server 2003 or Windows 2000 Server. And, computers that are running Windows Server 2003, Windows XP, and Windows 2000, cannot call the OpenCluster function against a cluster that is running Windows Server 2008. To remotely manage these clusters, use the Failover Cluster WMI provider.
For more information about the Failover Cluster WMI provider, visit the following Microsoft Web site:
Note This behavior does not occur if you call the OpenCluster function from Windows Server 2008.