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When two domain controllers are running Windows Server 2008 x64 Edition in two different networks that are connected by using Microsoft Internet Security and Acceleration (ISA) Server 2006, the domain controllers cannot replicate to each other.
This problem occurs because Windows Server 2008 x64 Edition uses a new remote procedure call (RPC) marshaling format (NDR 64) that the ISA Server 2006 RPC filter does not recognize. This problem still occurs even if you have disabled strict RPC for the rule or for the RPC filter.
To resolve this problem, apply the hotfix that the following Microsoft Knowledge Base article describes:
949314 Description of the ISA Server 2006 hotfix package: March 4, 2008
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
This problem occurs when two Windows Server 2008 x64 Edition-based computers have any RPC communication through ISA Server 2006. For example, if the local computer and the remote computer are both running Windows Server 2008 x64 Edition, you may not be able to remotely configure Disk Management of the Computer Management snap-in.
For more information about software update terminology, click the following article number to view the article in the Microsoft Knowledge Base:
824684 Description of the standard terminology that is used to describe Microsoft software updates