Tenable enforces a strict one‑license‑per‑instance policy to ensure compliance and prevent unauthorized sharing. When you attempt to register a scanner in offline mode, the system expects the license to be available for that specific device. If the system detects that the activation code has already been used, it blocks the offline activation process and returns this error.

: When you activate Nessus on a system, that system becomes the "active" instance. Subsequent attempts to use that code on another machine will trigger the "already in use" message. How to Resolve the Error

After the license is accepted, remember that you will also need to manually download and install the latest plugin set ( all-2.0.tar.gz ) since the machine has no internet access to pull them automatically. Pro-Tips for Avoiding Future License Issues

You must manually release the license through the Tenable Support Portal or Community site. Tenable Community Support Portal My Products (usually in the upper right corner). your Nessus Professional or Expert product in the list. Select "Reset Product Activation" or click the option next to the specific activation code.

The "License already in use" error typically occurs when Nessus detects that the license file has already been activated on another system or scanner. This error can be caused by:

on the machine currently holding the license. Navigate to the Nessus installation directory : Windows: C:\Program Files\Tenable\Nessus\ Linux: /opt/nessus/sbin/ Run the de-registration command : nessuscli fetch --challenge Use code with caution. This will give you a challenge code.

Copy the provided URL on that page to manually download the all-2.0.tar.gz plugins file later if needed. Step 4: Register the License on the Offline Scanner

Select your product type (e.g., Nessus Professional) from the left menu.

: Click My Products in the upper right corner.

Copy the long string of alphanumeric characters displayed in the output. Step 3: Download the License and Plugins

The error is a classic symptom of hardware identity mismatch in air-gapped environments. It is not a bug—it is a security feature preventing license theft. However, it is a frustrating feature when legitimate hardware fails or gets cloned.

The fastest and most reliable way to clear the error is by manually resetting your activation code through your Tenable account.

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

A link to download the ( all-2.0.tar.gz ).

With your license reset on the portal and a fresh challenge string in hand, you can now complete the offline activation without errors.

Paste your newly generated into the first box.

Before diving into the error, let's briefly discuss Nessus offline activation. When you purchase a Nessus license, you're provided with a license file that needs to be activated on the Nessus scanner. Online activation is a straightforward process that involves uploading the license file to the Nessus server, which then verifies the license and activates it. However, in offline environments or situations where internet connectivity is restricted, offline activation is necessary.

: Select your product type (e.g., Nessus Professional) and click Manage Product next to the specific license. Perform Reset : Click the Reset Product Activation link.

Transfer the downloaded files to your isolated Nessus host via secure media. Apply the License File