A sudden crash on the host machine prevents the license from being cleanly unlinked.
: Go to Settings > License and enter your Activation Code. nessus license already in use
| Cause | Explanation | |-------|-------------| | | Old installation still registered with Tenable; new installation tries same key. | | Cloning a VM | Copying a VM with Nessus installed duplicates the instance ID → license conflict. | | Changing hostname drastically | Some license types (especially lower-tier like Nessus Professional) tie to host identifier. | | Moving Nessus to a new server | If you didn’t deactivate before migration, the old registration remains active. | | License sharing between teams | Accidentally using the same key on multiple scanners in an organization. | | Tenable licensing server desync | Rare, but a stale record can falsely mark license as in-use. | A sudden crash on the host machine prevents
If the code is truly locked to another machine ID, this will fail with the same error, confirming you need to use or Fix #2 . | | Cloning a VM | Copying a
Keep reinstalling Nessus hoping it works – each new install generates a new instance ID and will keep hitting the same error until the original registration is cleared.
: If you are locked out due to frequent host changes, you must contact Tenable Support for a manual reset.