If you’re seeing the error during an offline activation of Nessus (Nessus Professional or Tenable.sc), it usually means the license file or challenge code is tied to a previously activated instance—even if that instance no longer exists. Here’s how to resolve it.
There is a limit on how frequently you can reset the code this way; if blocked, you must contact Tenable Support. 2. Generate a New Challenge Code
Encountering the error during the offline activation of Tenable Nessus is a frequent issue, especially for security professionals and IT administrators working in air-gapped or restricted environments. This article will dissect the core reasons behind this error, walk you through multiple proven solutions, and explain the differences between offline and online license management. nessus offline activation license already in use
In virtualized environments (VMware, Hyper-V, KVM), ensure that the network adapters assigned to the Nessus VM are set to a Static MAC address rather than dynamic. A shifting MAC address will alter the challenge code and break offline validity.
Key points to understand about Nessus licensing: If you’re seeing the error during an offline
You might think you have deactivated a license, but the process may not have completed successfully. A forgotten active registration on an old virtual machine or a recycled test server can hold the license and prevent its reuse.
Do not use an old challenge code. Generate a fresh one from the target machine. Open a terminal and run: /opt/nessus/sbin/nessuscli fetch --challenge Use code with caution. On Windows: Open Command Prompt as Administrator and run: Navigate to the section.
Before you can generate a new offline license file ( nessus.license ), you must release the active lock from your Tenable account. Log into the Tenable Community Portal. Navigate to the section.
