Nessus Offline Activation License Already In Use

What (Windows or Linux) is your offline Nessus scanner running on?

Background: how offline activation works (concise) nessus offline activation license already in use

If you cannot deactivate via the portal, back up your scan data, reset the Nessus installation, and contact Tenable Support with both the old and new challenge codes. With proper deactivation discipline, you will never see this error again. What (Windows or Linux) is your offline Nessus

A previous Nessus instance was deleted or shut down permanently without transferring or unregistering the license. Step-by-Step Solutions to Resolve the Error back up your scan data