This article describes how to fix an error that occurs when activating a license with the same license (.lic) file used previously: 'duplicate license has been detected'.
Scope
FortiWeb.
Solution
1) Wait for 90 minutes and retry uploading the license file.
Note: It may take up to 24 hours for the systems to be updated. If it still fails after 90 minutes, wait and retry.
2) Delete or shut down the old virtual machine for 6 to 24 hours.
3) Download a fresh copy of License file from support.fortinet.com and use it on a new VM instance.
