If the Defender Security Server service has been shut down or stopped incorrectly, this may cause an issue with the "Store and Forward" file. This file is in the configured Log folder and is named with an extension of ".LogQueue.dat".
On the affected server, locate the Log folder configured in the Defender Security Server Configuration. The default location for the Log folder is "C:\Program Files (x86)\Quest Software\Defender\DSS Active Directory Edition\Logs".
This Log folder should have a file with an extension of ".LogQueue.dat", and a prefix of the Fully Qualified Domain name of the server. Please rename this "<FQDN>.LogQueue.dat" file by adding ".old" to the end of the file. The Defender Security Server service should now be able to start correctly.
To prevent this issue, please ensure that the Defender Security Server version is 184.108.40.20628 (or higher), as these versions contain a fix (#4751) related to better handling of the "Store and Forward" file.
The latest Defender Security Server hotfix can be downloaded here: https://support.quest.com/defender/download-new-releases.