This error typically occurs in several common scenarios:

In the context of Nessus, the error "License already in use" typically indicates that the activation code you are trying to use has already been registered to another scanner instance or was previously activated on a different device.

Enter the activation code provided by Tenable (via email for free versions or from your purchase confirmation for paid licenses) along with the challenge code generated in Step 2.

With a reset license and a new Challenge Code, you can now generate the license file. Go to the . Enter your Activation Code (the one you just reset). Paste your New Challenge Code . Click Submit and download the nessus.license file. Copy this file to your offline machine. Step 4: Apply the License and Plugins

Troubleshooting the "Nessus Offline Activation License Already in Use" Error

When you reach the offline activation portal, you will be asked to provide an (your license key) and a Challenge Code , which is a unique string generated by your offline Nessus server. The portal uses this information to generate a license file ( nessus.license ). You then transfer this file back to your offline server to finalize the activation.

Method 1: Reset the Activation Code via Tenable Community Portal

This is often the quickest solution if the error is due to a system conflict that cannot be easily resolved.

Moving a Nessus VM to a new host often changes the hardware UUID, triggering a license mismatch. Step 1: Reset the Activation Code

: Transfer the nessus.license file to the offline machine and register it using the command line: