A cPanel & WHM License might show the following error:
The cPanel license server replied that the license has been activated on too many machines (600)
As the cPanel software licensing is based upon IP addresses, the license could become locked due to the license system seeing the license activated on too many systems. For example, if the license is moved several times, it may lock it. It is also possible to get a locked license if cPanel is installed many times within a short period of time.
To ensure that a license is being used on only one server, the cPanel license system checks certain attributes upon contacting the cPanel license servers. If these attributes are inconsistent between calls to the license servers, it will cause a license to lock.
For locked license issues with the software after the installation, it is best to open a support ticket.