You wiped the OS (Windows/Linux) and reinstalled Nessus. The hostname or network configuration changed slightly. The new Challenge Code does not match the old one. Tenable rejects the attempt because your license key is already "Checked out" to the previous OS install.
When attempting a Nessus offline activation, the error indicating a license is "already in use" occurs because Tenable activation codes are restricted to one active host at a time . To resolve this,
Modifying the virtual machine (VM) resources, changing the Network Interface Card (NIC), or updating the OS MAC address, which alters the Challenge Code. nessus offline activation license already in use
Offline scanners require manual plugin updates. Follow the guide at Tenable Software Updates Are you performing a fresh installation , or are you trying to an existing license to a new air-gapped machine? Update License Offline (Tenable Nessus 10.11)
: C:\Program Files\Tenable\Nessus\nessuscli.exe fetch --challenge You wiped the OS (Windows/Linux) and reinstalled Nessus
Are you to a new machine, or did this happen unexpectedly on an existing system?
If the previous Nessus installation is still running and accessible, you can cleanly unregister the license locally. This frees up the activation code instantly. Tenable rejects the attempt because your license key
A unique hardware string generated by your specific Nessus installation.
This command generates a challenge code if the license is not registered. If the license is already in use on another host, the Nessus service logs will contain specific error codes that you can provide to Tenable Support if needed.
