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Last update: . Author: Cyril LEROY .

Lync Front-End Service is Reported Down due to User Authentication Test Failure

When scanning a Lync Front-end service, GSX Monitor may fail to run a User Authentication test, due to the Lync servers variable MaxEndPointsPerUser's maximum value being reached. The value of this can be set using the Lync server PowerShell commands (by default the value is four). This value represents the maximum number of connections that can be made to the Lync server with the same credentials.

Below we will look at specifying a test user for each server configured, so that we do not run a test command with the same user name concurrently.

GSX Monitor 10.9+ | Lync Server 2013


  • Front-end Service is reported Down: User Authentication test failed. 
  • User Authentication: Another endpoint with the same endpoint id or gruu already exists for the specified uri. 

How to Solve the Issue

To prevent GSX Monitor from issuing multiple Test-CSClientAuthentication cmdlets with the same user account, configure a dedicated test user for each server.

  1. Select the server in the main view of GSX Monitor.
  2. Open the server configuration (Ctrl+E).
  3. From the Connectivity tab, enter a unique user name in the highlighted section:
    Lync Connectivity
  4. Once you have entered the unique user, save the configuration and allow GSX Monitor to scan.
  5. Check that the User Authentication test error is no longer triggered.

Possible Workaround

The GSXScanEngine.exe settings can be changed to prevent Lync scans to be executed concurrently:
1. Shut down GSX Monitor including all background processes.
2. Using Windows File Explorer navigate to the GSX Monitor\Data\ folder.
3. Open the GSXScanEngine.ini file in a text editor.
4. Locate the [OPTIONS] section:

  • if the LYNC_OPTIONS line already exists, add the following at the end of the line: ;OPTIONS;MODEMULTIMNGR=0 and make sure all entries are separated by a semicolon.
  • If the LYNC_OPTIONS line does not exists, add LYNC_OPTIONS=;OPTIONS;MODEMULTIMNGR=0 anywhere in the [OPTIONS] section.

5. Save and Close the file.
6. Restart GSX Monitor including the Windows Service to load the changes.

Changing this option to scan one Lync server at a time may considerably increase the time to scan all Lync servers. Consider using multiple test users in a large environment rather than changing this option.

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