I was following the steps from the documentation for manual activation.

When passing from one window to the other, in order to copy the "Machine name" and the "Machine info key", I have put the "Machine Name" in the "Machine info key" field and reciprocally. It's a bit confusing because in Test Studio Ultimate the two fields are in a particular order and in the Key management page they are in reverse order. That would be a suggestion of improvement for the activation process: set the same order for these fields both in test studio ultimate and in this page.