Error: "The server is not operational"

If you face an issue "The server is not operational" while executing Active directory queries or using tool which connect to Active Directory, you will need to check the connectivity with the active directory.
In order to resolve the issue follow the steps mentioned in the KB article http://support.microsoft.com/kb/325322
If still issue persist you will need to check domain DNS entries. Check if forward and reverse look-up entries are populated correctly, for the active directory domain you are trying to connect.
If above steps does not resolve the issue and if you programatically connecting to active directory then try to use cached connections for the different queries.