Fix Azure AD Connect Installation that Stopped Working After a Reboot Error 9903 SQLLocalDB 15.0 Error 575

I have been getting messages from admins whose Azure AD Connect installations stopped working after installing the latest Windows Server cumulative update. I find that the Azure AD Connect-managed LocalDB solution couldn’t start anymore after any reboot; Azure AD Connect didn’t break because of the monthly cumulative update; the update was merely the cause for the reboot.

Cause

In all cases in which the issue was reproduceable, the same two artifacts can be witnessed:

1. In the error.log file, typically located at C:\Windows\ServiceProfiles\ADSync\AppData\Local\Microsoft\Microsoft SQL Server Local DB\Instances\ADSync2019, the following log lines can be read:

Error: 9903, Severity: 20, State: 1. The log scan number (x) passed to log scan in database 'model' is not valid. This error may indicate data corruption or that the log file (.ldf) does not match the data file (.mdf). If this error occurred during replication, re-create the publication. Otherwise, restore from backup if the problem results in a failure during startup.

2. An event is logged in the Application log with Event ID 528:

Event 528 with source SQLLocalDB 15.0:

Windows API call WaitForMultipleObjects returned error code: 575. Windows system error message is: {Application Error} The application was unable to start correctly (0x%lx). Click OK to close the application. Reported at line: 3714.

Solution

If you experience this issue, you can have your Azure AD Connect installation working again with these steps, using an elevated Windows PowerShell:

Step 1: Stop the Microsoft Azure AD Sync service:
Set-Service ADSync -StartupType Disabled
Stop-Service ADSync -force

Step 2: Copy over the known-good model database template:

Copy-Item "C:\Program Files\Microsoft SQL
Server\150\LocalDB\Binn\Templates\model.mdf"
"C:\Windows\ServiceProfiles\ADSync\AppData\Local\Microsoft\Microsoft SQL Server Local DB\Instances\ADSync2019"
Copy-Item "C:\Program Files\Microsoft SQL
Server\150\LocalDB\Binn\Templates\modellog.ldf"
"C:\Windows\ServiceProfiles\ADSync\AppData\Local\Microsoft\Microsoft SQL Server Local DB\Instances\ADSync2019"

Step 3: Start the Microsoft Azure AD Sync service:

Set-Service ADSync -StartupType Automatic
Start-Service ADSync

The location of Azure AD Connect’s service profile (“C:\Windows\ServiceProfiles\ADSync\AppData\Local\Microsoft\Microsoft SQL Server Local DB\Instances\ADSync2019”) could be different in your situation. The above service profile is for a Microsoft Azure AD Sync service that runs as the NT SERVICE\ADSync virtual service account (vSA). This is the default account to run the service. If you run the service as another account or as a group Managed Service Account, change the account name in the service profile location above.

To no longer experience this issue, upgrade Azure AD Connect to version 2.1.1.0, as the Azure AD Connect team have added logic to this version of Azure AD Connect to prevent the issue from occurring.