I ran in to this one awhile back but had to figure it out again recently.
Customer has a root DFS Name Space on a single server. He decommissioned the server without removing the name space first. Now his login scripts are failing and he want the name space back but the server has been reinstalled. Quickest way is to delete the name space and recreate it on another server but that’s the problem, deleting the name space. To delete the name space you need to start up adsiedit and go to CN=Dfs-Configuration,CN=System,DC=<name_of_your_domain>. On the server that you are creating the new name space you need to execute the following commands:
Dfsutil /PktFlush
Dfsutil /SpcFlush
Dfsutil /PurgeMupCache
Now you should be able to create the same name space on the new server. I do highly recommend that you wait 15 min before doing so. DFS stops giving referrals to the decommissioned server within 15 minutes of the update to the DFS Active Directory directory service object. The DFS Active Directory object resides on the local domain controller and is issued by the PDC emulator master. The time that the update can take depends on Active Directory replication schedules.