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How to Fix Azure AD Connect Stopped Extension DLL Exception
Question details
The user needs to resolve an Azure AD Connect synchronization failure caused by a stopped-extension-dll-exception error.
- Product
- Azure AD Connect
- Device & OS
- not provided
- Scenario
- Synchronizing local Active Directory with Microsoft Entra ID after server downtime or a credential change.
- Observed behavior
- The directory synchronization process fails and displays a stopped-extension-dll-exception error.
Before troubleshooting, ensure you have Global Administrator or Hybrid Identity Administrator privileges in Microsoft Entra ID, as well as local administrator rights on the Azure AD Connect server.
Verify Synchronization Credentials and Network Access
The most common causes of this error are expired credentials or blocked network connections to Microsoft endpoints.
Azure AD Connect requires seamless communication with Microsoft Entra ID. If passwords change or network rules are modified while the server is offline, the synchronization process will fail upon restart.
Log in to the Microsoft Entra ID portal and verify that the synchronization account password is correct, active, and has not expired.
Verify DNS resolution on your server and ensure that your network firewall rules allow outbound traffic to all required Microsoft Entra endpoints.
Log into the Microsoft 365 admin center and navigate to the Service Health portal to ensure there are no ongoing identity service incidents affecting synchronization.
Update and Restart Azure AD Connect Services
Restarting the sync services or applying the latest application update can resolve transient errors causing the DLL exception.
Perform a Full Initial Synchronization
If standard troubleshooting fails, forcing a full initial synchronization can rebuild the connection state.
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Frequently Asked Questions
Why does the stopped-extension-dll-exception error happen?
This error typically occurs when the synchronization server experiences sudden downtime, loses network connectivity to Microsoft endpoints, or when the synchronization account credentials in Microsoft Entra ID expire or change unexpectedly.
How long does a full initial synchronization take?
The duration depends on the total number of objects (users, groups, and devices) in your local Active Directory. It can range from a few minutes for small environments to several hours for large enterprise directories.
Can a firewall cause Azure AD Connect synchronization to fail?
Yes. If your organization's firewall rules block outbound traffic to Microsoft Entra ID endpoints, Azure AD Connect cannot communicate properly, resulting in connection timeouts or extension DLL exceptions.
How do I check if my Azure AD Connect version is outdated?
You can check your version by opening the Windows Control Panel, navigating to Programs and Features, and locating 'Microsoft Azure AD Connect' in the list. Compare its version number with the latest release notes available on the Microsoft documentation website.
