Several team members have access to the Tenable license portal. Someone else on your team already used the activation code to generate an offline license for a different server (e.g., a backup scanner in a data center). You are now trying to use the same code for a new office scanner.
If your old server is dead, decommissioned, or lost, you must release the license lock on Tenable’s side. nessus offline activation license already in use
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. Several team members have access to the Tenable