Error upgrading Microsoft Entra Connect Sync - An error occurred while upgrading from Azure Active Directory Synchronization Service

Question

An error occurred while upgrading from Azure Active Directory Sync. Unable to upgrade the Synchronization Service. Please see the event log for additional details.

I'm not sure how much of the logged messages to include here, so I'll just start with the first few lines. Prior to a couple of weeks ago, the system had been running well. Then, I noticed a few new users in our on-premise AD weren't syncing. Azure AD Connect is running on server 2019.

In the event log, I see Event ID 905:

Scheduler::SchedulerThreadMain : An error occured and scheduler run failed to perform all operation.

System.Management.Automation.CmdletInvocationException: <error>E_MMS_UNSUPPORTED_SCHEMA_UPDATE</error> ---> Microsoft.IdentityManagement.PowerShell.ObjectModel.SynchronizationConfigurationValidationException: <error>E_MMS_UNSUPPORTED_SCHEMA_UPDATE</error>

Event ID 906:

SetADSyncGlobalSettingsCmdlet Exception Microsoft.IdentityManagement.PowerShell.ObjectModel.SynchronizationConfigurationValidationException: <error>E_MMS_UNSUPPORTED_SCHEMA_UPDATE</error>

at Microsoft.IdentityManagement.PowerShell.Cmdlet.SetADSyncGlobalSettingsCmdlet.ProcessRecord().

Any suggestions on where to even begin?

Answer 1

Hello John Wheeler,

Greetings! Thanks for raising this question in the Q&A forum.

The error code E_MMS_UNSUPPORTED_SCHEMA_UPDATE is a metaverse schema validation failure, not a connectivity or credentials issue. When the setup wizard upgrades Azure AD Connect, it compares the original out-of-box metaverse schema file (mv.dsml) against the schema that is currently active on your server. If it finds attribute bindings that were added outside the standard configuration path, for example custom extension attributes, third-party provisioning tools, or a manual database edit made at some point in the past, the wizard cannot safely merge them and the upgrade aborts with this error rather than risk corrupting your sync engine. The recent syncing issue with new users not appearing is very likely unrelated to the upgrade error itself, and is probably a separate, smaller sync scoping or filtering issue that started around the same time.

1. Back up your current configuration before touching anything. On the Entra Connect server, open PowerShell as administrator and run:

Export-ADSyncConfiguration -Path "C:\ADSyncBackup"

This preserves your current sync rules, connectors, and settings in case anything needs to be rolled back.

1. Find the exact attribute bindings causing the mismatch. Open the latest trace log in C:\ProgramData\AADConnect\ and search for EncodeMetaverseExtensions. You will see a comparison similar to this pattern:

Metaverse schema [ORIGINAL] - object types (5), attribute definitions (226)
Metaverse schema [CURRENT] - object types (5), attribute definitions (245)
Existing object type [person], with [19] new schema bindings.

The lines following this list every extra attribute (for example extension_employeeID, extension_extensionAttribute1 through 15) that were added to the metaverse beyond the stock schema. This list is exactly what is blocking the upgrade.

Open Synchronization Service Manager and review the Metaverse Designer tab. Go to Start > Synchronization Service (or run miisclient.exe from C:\Program Files\Microsoft Azure AD Sync\UIShell), select the Metaverse Designer tab, and locate the attributes identified in step 2 under the person object type.

Decide whether each flagged attribute is still needed. If these extension attributes were added intentionally to support a business process such as employee ID sync or a custom application, do not delete them outright, since removing an attribute that is actively used in a sync rule will break that flow. If they are leftover from an old customization that is no longer used, they can be safely removed from the Metaverse Designer to bring the schema back in line with the stock version, which allows the upgrade to proceed.

Retry the upgrade after the schema is reconciled. Rerun the Microsoft Entra Connect installer once the extra attribute bindings have been resolved or removed.

If the custom attributes must be retained, this becomes a case for Microsoft Support rather than a self-service fix, since a supported schema merge that preserves custom bindings during upgrade requires their assistance. Open a support request through the Azure portal under Help + support, category Directory and identity > Entra Connect, and attach:

• The trace log showing the EncodeMetaverseExtensions comparison
  • The exported configuration from step 1
    • Your current Entra Connect version and the version you are attempting to upgrade to

Reference documentation: Troubleshoot Microsoft Entra Connect upgrade issues Microsoft Entra Connect: Version release history

If this answer helps you kindly accept the answer which will help others who have similar questions.

Best Regards,

Jerald Felix.