Cannot Access Windows 2008 R2 Member Servers From The DMZ Zone to the Internal Network Domain Controller

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http://serverfault.com – I have 2 Sharepoint Servers and 1 Fast Server(All Windows 2008 R2) moved From Internal Network To The DMZ layer. Now these 3 servers cannot communicate with the DC & DNS(Windows 2000). All the related ports have been open from the Firewall WatchGuard both ways. But i can ping the DC & DNS. I can access the shared folder on both the DC & DNS. Login is too slow, When i try to add a domain user to local administrators group, the following error occurs: Error: RPC Server is Unavailable. Event Log Error: **The processing of Group Policy failed. Windows could not resolve the user name (HowTos)