For example, Microsoft clients communicate with Microsoft Exchange Server using RPC.The client computer sends a message to the server computer with certain arguments.For clarity, in this article, the machine initiating RPC communication will be designated the client, and the machine with which it communicates will be the server.Remote Procedure Call (RPC) is a mechanism that allows Windows processes to communicate with one another, either between a client and server across a network or within a single system. RPC uses dynamic ports for communication between systems, but a static port (TCP port 135) must also be used as a starting point for communication. This condition may be caused by a DNS lookup problem.RPC itself has no special insight into failures but attempts to map lower layer protocol failures into an error at the RPC layer.It's best practice to sync from the domain environment. If it is you need to make sure you have the "Time Synchronization" Integration service disabled.
But before I talk about the specific RPC errors and solutions, let’s get a solid grounding in RPC terminology."The RPC server is unavailable" is a fairly common error in Windows that can occur in a wide variety of situations, most of them involving communication between two machines across a network.It can also occur during local operations on a machine, however.If you are unable to sync with any of the public NTP servers (and assuming they resolve to valid IPs using the nameserver on your network) you have a network level issue.Check all firewalls between you and the internet (a wireshark traffic dump like John suggested in his comments on the question would be a good idea too - if the firewalls are returning the ICMP "Communication prohibited by filter" message that would tell you which firewall is saying no.) Is this server part of a domain?command can validate DNS health of domain controllers that run Windows 2000 Server (SP3 or later), Windows Server 2003, Windows Server 2008, and Windows Server 2008 R2.