In addition to keeping up with your Sitecore license, any Sitecore installation running Keystone must also have an active Keystone license present in the web root folder. Otherwise, you will get an error like the following:
Keystone License – Error
No valid Keystone license can be found. Please ensure the .lic file is in the webroot and the App Pool has access to read the file. If you have placed the file and corrected permissions a restart of the app pool and site may be required.
No licenses found.
If you have already placed the license file (.lic) in your site’s web root folder and are still receiving an error, your license file may have expired. This is especially common for the Keystone trial licenses. At the time of writing, there is not currently a way I can find to view the expiry information for a license file. You will need to contact Keystone support to have them review your license file.
If your license is expired, there are two solutions to resolve the error. You can purchase an updated official product license or you can uninstall all Keystone components. Once Keystone isn’t in your solution, its licensing logic cannot execute and therefore the license error will go away.