Bruno is right and I would like to add that this is enforced in practice by e-on's registration method. When you install Vue on a machine, it'll give you the installation code, which you then have to take to their site and get an activation code. Only then the software will run normally. If you install Vue on a second machine, you'll get another installation code but when you try to obtain the activation code, it'll tell you that this serial number is already registered and can not be registered twice. So, you have to contact e-on and tell them your situation and then they'll allow for a second activation code.

Note: in case you were wondering, you can not use the same activation code on both machines because this is linked to the installation code, which is different for both machines, although the serial number is the same.