If the problem persists after trying these steps, open a support ticket with Tenable. Provide them with your Activation Code and the output of nessus-fetch --challenge . They can manually clear the lock from their backend database.
The error message "License Already in Use" or "Code in Use" is Tenable's mechanism to prevent license piracy across multiple devices. While this protects the software developer, it can be a nuisance for legitimate users. Here are the most common reasons for this error: nessus offline activation license already in use
Run nessuscli fetch --code-in-use to check status, and unregister old instances before building new ones. If the problem persists after trying these steps,
Once you have the reset activation code and the new challenge code: On a machine with internet access, go to the Nessus Offline Registration page Enter your Challenge Code Activation Code , then click Download the nessus.license The error message "License Already in Use" or
/opt/nessus/sbin/nessuscli fetch --register-offline nessus.license