Sources
Delphi Russian Knowledge Base
DRKB - это самая большая и удобная в использовании база знаний по Дельфи в рунете, составленная Виталием Невзоровым

Error: RPC Server is unavailable

01.01.2007

The error is usually caused because the server can't be located.  Make sure you can ping the server machine using the string you typed into the ComputerName property of the TRemoteServer.   You might also want to try using an IP address instead in case there is some problem with your DNS configuration or the hosts file.  Try setting the "Default Authentication Level" to  (Run DCOMCNFG on the server to do this.)  Lastly, check the Microsoft Developer's Network on the Web for the latest information on this Microsoft transport.  The MSDN can be located at the time of the writing at www.microsoft.com/msdn.