Question : RPC server unavailable on adding host to Cluster

I'm getting an error message of "The RPC server is unavailable on the specified computer" when I attempt to add another host in the same domain in the Cluster .... I have 2 servers, both have 2 NICs and are in subnets 10.x.x.x (Public) and 192.x.x.x (Private) respectively. Both can ping each other. However, the Private NIC i.e. 192.x.x.x shows unidentified network against it and I dont know why is that !
Anyway, I browsed around and found that changing mode to multicast can overcome this issue ; so i removed the node and added it by selecting multicast but still no joy !
Platform is Windows Server 2008 ...

Answer : RPC server unavailable on adding host to Cluster

Which IP are you typing to add it to the cluster.  10. or 192. ?