Error 8418 after schema extension for Exchange 2010

After you have run setup /PrepareSchema to make modifications to the Active Directory schema, as a preparation for an Exchange 2010 installation, the following errors may occur on your domain controller(s):

Log Name:      Directory Service
Source:        Microsoft-Windows-ActiveDirectory_DomainService
Event ID:      1791
Task Category: Replication
Level:         Error
Computer:   server2
Replication of application directory partition DC=my,DC=domain,DC=com from source abc (server1) has been aborted. Replication requires consistent schema but last attempt to synchornize the schema had failed. It is crucial that schema replication functions properly. See previous errors for more diagnostics. If this issue persists, please contact Microsoft Product Support Services for assistance. Error 8418: The replication operation failed because of a schema mismatch between the servers involved..


Log Name:      Directory Service
Source:        Microsoft-Windows-ActiveDirectory_DomainService
Event ID:      1955
Task Category: Replication
Level:         Information
Computer:      server2
Active Directory Domain Services encountered a write conflict when applying replicated changes to the following object.

CN=Address Lists Container,CN=domain,CN=Microsoft Exchange,CN=Services,CN=Configuration,DC=my,DC=domain,DC=com

Event log entries preceding this entry will indicate whether or not the update was accepted.

A write conflict can be caused by simultaneous changes to the same object or simultaneous changes to other objects that have attributes referencing this object. This commonly occurs when the object represents a large group with many members, and the functional level of the forest is set to Windows 2000. This conflict triggered additional retries of the update. If the system appears slow, it could be because replication of these changes is occurring.

User Action
Use smaller groups for this operation or raise the forest functional level to Windows Server 2003.

If you very recently ran the setup /PrepareSchema command, these errors are normal. The Schema Extension can take a while; in my case it took 30 minutes.

To verify the status of the replication, you can use the following commands on Windows 2008:

repadmin /showrepl : Displays the replication status
repadmin /replsummary : Summarizes the replication state and health

To force a replication between your domain controllers, run the command repadmin /syncall
However, as long as the schemas do not match, no replication will find place.

You can also use Active Directory Sites and Services to replicate your domain controllers.

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