RPC Server Unavailable

[V for Vinsanity]

I am on a Windows 2003 with SP1 domain controller and if I am trying to run repadmin /syncall /p /e, then I am getting "RPC sever unavailable" error. This DC is the only one on this site that is connected via a VPN. I did try to solve the packets drop issue, but still the error comes up. There are no problems in DNS, as the other Server is easily accessible. The error that I am getting in event logs is posted below:

Event Type: Error
Event Source: NTDS Replication
Event Category: Replication
Event ID: 1864
Date: 9/21/2007
Time: 11:03:59 AM
User: NT AUTHORITY\ANONYMOUS LOGON
Computer:
Description: This is the replication status for the following directory partition on the local domain controller.

[techman]

It could be that because of some firewall, the network traffic might be getting rejected that usually originates from Windows Server 2003 Service Pack 1, based or Windows Vista based computers, check for some more refrence here - http://support.microsoft.com/kb/899148/EN-US/