The system cannot log you on due to the following error: The RPC server is unavailable || Windows Server 2003

Try Bellow :
   1. Incorrect DNS settings.

     2. Incorrect Time and Time zone settings.

     3. The "TCP/IP NetBIOS Helper" service isn't running.

     4. The "Remote Registry" service isn't running

then restart.

If not work then.
1. Take backup of registry
2.
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Terminal Server

create DWORD then put Hex value=1
IgnoreRegUserConfigErrors =Dword:1