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MarcoMangianteIM's avatar
MarcoMangianteIM
Brass Contributor
Sep 19, 2025

Microsoft Entra Connect sync stopped, request upgrade and library not found

Hello,

I have the latest (for our company, present on Entra blade) version of Microsoft Entra Connect Sync: 4 days ago I noticed on Synchronization Service Manager that there is no sync of data; I have started the Microsoft Entra Connect Sync and found a big button with "Upgrade" word; I tried to execute the upgrade but when the it arrives to the Connect to Microsoft Entra ID step, I fill with my global administrator account but found a stop error:

 

An error occured while retrieving the Active Directory schema. The error was: Could not load file or assembly 'file:///C:\Program Files\Microsoft Azure AD Sync\Bin\Microsoft.IdentityModel.Clients.ActiveDirectory.dll' or one of its dependencies. The system cannot find the file specified.

 

and when I click again on Next I have the same request of global administrator user and password and the same error. 

Now, the library is not present but I verified, in a test tenant where I have a working Entra Connect Sync system, that the files is not present even there (and also when I start Microsoft Connect Entra Sync I haven't the upgrade button there); I also tried to repair the installation, but obviously the file is no there.

 

What can I do? Are there other people with the same issue? Any idea is appreciated.

Azure AD Connect
hybrid
On-Premises

1 Reply

  • Kidd_Ip's avatar
    Kidd_Ip
    MVP
    Sep 20, 2025

    Please try this:

     

    1. Check for Inconsistent Installer Packages
    • Open %ProgramData%\AADConnect\ and inspect the latest installation trace log.
    • Look for entries like GetInstalledPackagesByUpgradeCode to identify if older versions are still registered.
    • If the wizard detects remnants of older installations, it may trigger the upgrade button unnecessarily.
    1. Manually Remove Corrupt Install Entries
    • Use msiexec /x {ProductCode} to uninstall any ghosted or partially removed packages.
    • Be cautious, do not edit the registry directly unless guided by Microsoft support.
    1. Reinstall Microsoft Entra Connect Cleanly
    • Download the latest version from the  official Microsoft Entra Connect page.
    • Uninstall the current version completely.
    • Reboot the server.
    • Install the new version and reconfigure sync.
    1. Verify .NET and Dependencies
    • Ensure that the required .NET Framework version is installed and healthy.
    • Use sfc /scannow to check for system file corruption.
    1. Check for DLL in NuGet or SDK
    • The missing DLL (Microsoft.IdentityModel.Clients.ActiveDirectory.dll) is part of the Azure AD Authentication Library (ADAL).
    • You can manually download it from  NuGet and place it in the expected path, but this is a workaround and not officially supported.

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