Upgrade to MS Entra Connect Sync fail

Error `14001` during Microsoft Entra Connect Sync upgrade is usually related to a corrupted or missing Visual C++ runtime dependency (Side-by-Side configuration issue).

A few things you can try:

1. Check the exact SideBySide error in Event Viewer:

* Open `Event Viewer`

* Go to:

`Windows Logs > Application`

* Look for events with source:

`SideBySide`

hose events usually indicate which Visual C++ package or DLL is missing.

2. Install the latest supported Visual C++ Redistributable manually.

Microsoft now provides a unified package for 2015-2022:

* x64:

[Visual C++ Redistributable 2015-2022 (x64)](https://aka.ms/vs/17/release/vc_redist.x64.exe?utm_source

* x86:

[Visual C++ Redistributable 2015-2022 (x86)](https://aka.ms/vs/17/release/vc_redist.x86.exe?utm_source

Install both x64 and x86 versions even on Server 2022.

3. Reboot the server after installation.

4. Run system repair checks:

DISM /Online /Cleanup-Image /RestoreHealth

sfc /scannow

```

5. Verify .NET Framework health:

Get-WindowsFeature *NET*

```Aso ensure the latest .NET updates are installed.

6. Temporarily disable antivirus/EDR during upgrade if applicable.

7. Before reinstalling Entra Connect Sync:

* Export current configuration

* Confirm staging/backup availability

* Verify SQL LocalDB service is healthy

You can also completely clean leftover Entra Connect components using:

Get-WmiObject Win32_Product | Where-Object {

$_.Name -match "Azure AD|Entra|Microsoft Identity"

} | Select Name

```Then uninstall remaining components manually if necessary.

Since you already have full backups, worst case you can restore the VM and perform a clean install of the latest Entra Connect Sync version.