In your OP you refer to reregistering the license, which gives you the message. There is no need to do that. The license exists on the dongle not a computer. You only need to register it to your dongle once, independent of what computer you are using. All you should need to do is install the eLicense software on the new computer and stick the dongle with the license on it into a USB port. Use the eLicense program to check that you have a valid license on the dongle.
You can use the license on the dongle to run Cubase on any system that has both Cubase and the eLicense software installed. You can move the dongle to work on different computers, even between Macs & PCs.