Upgrading Active Directory forest level throws the warning: “The functional level could not be raised. The error is: The directory service is busy.”

I ran into an interesting error that I’ve never seen before through the many times I’ve upgrade an Active Directory’s forest functional level where I would receive a:

The functional level could not be raised. The error is: The directory service is busy.

What’s interesting was that I had no problems upgrading the domain functional level prior to upgrading the forest functional level but of all the times I’ve had problems modifying schemas or objects in Active Directory, it almost always was due to communication problems between domain controllers so the first thing I did was use repadmin to see if any replication errors were logged:

C:\Program Files (x86)\Support Tools>repadmin /showrepl

repadmin running command /showrepl against server localhost

Default-First-Site-Name\DC1
DC Options: IS_GC
Site Options: (none)
DC object GUID: 1ca423a8-872b-4c84-be97-790149f515db
DC invocationID: 1ca423a8-872b-4c84-be97-790149f515db

==== INBOUND NEIGHBORS ======================================

DC=someDomain,DC=local
    Default-First-Site-Name\DC2 via RPC
        DC object GUID: 5fb9ecdd-a78e-4067-8299-0ce9fef9c076
        Last attempt @ 2011-04-19 22:27:58 was successful.

CN=Configuration,DC=someDomain,DC=local
    Default-First-Site-Name\DC2 via RPC
        DC object GUID: 5fb9ecdd-a78e-4067-8299-0ce9fef9c076
        Last attempt @ 2011-04-19 22:14:38 failed, result 1908 (0x774):
            Could not find the domain controller for this domain.
        1 consecutive failure(s).
        Last success @ 2011-04-19 21:53:49.

CN=Schema,CN=Configuration,DC=someDomain,DC=local
    Default-First-Site-Name\DC2 via RPC
        DC object GUID: 5fb9ecdd-a78e-4067-8299-0ce9fef9c076
        Last attempt @ 2011-04-19 22:16:02 failed, result 1908 (0x774):
            Could not find the domain controller for this domain.
        1 consecutive failure(s).
        Last success @ 2011-04-19 21:53:49.

DC=DomainDnsZones,DC=someDomain,DC=local
    Default-First-Site-Name\DC2 via RPC
        DC object GUID: 5fb9ecdd-a78e-4067-8299-0ce9fef9c076
        Last attempt @ 2011-04-19 22:18:26 failed, result 1908 (0x774):
            Could not find the domain controller for this domain.
        1 consecutive failure(s).
        Last success @ 2011-04-19 21:53:49.

DC=ForestDnsZones,DC=someDomain,DC=local
    Default-First-Site-Name\DC2 via RPC
        DC object GUID: 5fb9ecdd-a78e-4067-8299-0ce9fef9c076
        Last attempt @ 2011-04-19 22:30:10 was successful.

Source: Default-First-Site-Name\DC2
******* 1 CONSECUTIVE FAILURES since 2011-04-19 21:53:49
Last error: 1908 (0x774):
            Could not find the domain controller for this domain.

C:\Program Files (x86)\Support Tools>

After seeing that there were errors, I opened Replication Monitor and tried to force a replication to see if an error was logged and if there was, what the informational message was:

As shown in the above screenshot in Replication Monitor, the error message:

Replication Failure: The reason is: Could not find the domain controller for this domain.

… appears to suggest that DC1 is unable to contact DC2.  After plowing through the logs on the domain controllers, I ended up fixing a few things in DNS and the domain controller’s DNS settings to get replication working again.

Once the replication issues were gone, I was then able to upgrade the forest functional level.

Since replication problems can have many causes, if you experience the same error message as I did, I’d recommend checking Active Directory replication between your domain controllers with tools such as:

1. Replication Monitor
2. DCDiag
3. NetDiag

Hope this helps.