Defender 5.8.1 has been rebranded from Quest Software to Dell and therefore, the Program Files folder path has changed.
An upgrade from Defender 5.7 to 5.8.1 will update the Windows Firewall exception for "Defender Security Server" so that the path is changed from "C:\Program Files (x86)\Quest Software\Defender\DSS Active Directory Edition\DSServADE.exe" to "c:\Program Files\Dell\Defender Active Directory Edition\DSServADE.exe".
NOTE: The actual path should be C:\Program Files\Dell\Defender\Security Server\DSServADE.exe.
Previous Windows Firewall exceptions created manually, and pointing to the Defender Security Server executables in the old file location, will no longer be applicable to the new version.
Also, the scope for the firewall exception may not be set for the domain.
Please verify your Firewall configuration, to ensure there is an exception for the Defender Security Server, with the correct path, after the upgrade.
The default location for the Dell Defender Security Server Service in version 5.8.1 is:
C:\Program Files\Dell\Defender\Security Server\DSServADE.exe
If the scope for the firewall exception is not set for your domain, be sure to select this as well.