Beeps, you are correct, Service Center is only for registration. If there is a later version of GR that he is eligible for, he should download and install it. It's tiny, and a quick download/install, in addition to having internal beneficial updates to it.
If you want to save logging in twice, once you get to the NI site, go to the downloads section and log in there. If you log in on the main page, then go to downloads, it will make you log in again - silly, but that's how they built it.
That Service Center was always badly implemented. I have had Komplete 3 all the way through my current Komplete 8 Ultimate, and is only the last couple of them that they use an online Service Center mechanism. It used to install Service Center anytime you updated anything, which would be many times over if you had one of the Komplete products, as each of the more than a dozen component upgrades would not care that Service Center was already on your machine.
Go to the NI site
www.native-instruments.com, go to the updates, then log in, download the latest version of that component, install that component, then I think it takes you to the online service center. If that version of GR still loops in Service Center install, then just cancel out of that portion and go to the online Service Center. I believe if you have updated a component it may go through the activation again.
If all of that STILL does not work, and that has happened to me before once or twice with them over the years. TRIPLE check your registration info, then go to the manage account section - it used to be you could delete registrations, and then re-register them again. If the delete registration option is on the menu choices, then as long as your registration info is good, you will be able to reactivate properly.
Last recourse - call them. They can manually delete the registration and you can then go to Service Center online and activate.
In all of the above, run GR's activation in stand-alone run as admin mode prior to trying to use in any host, such as Sonar.
Bob Bone