In some cases when you are trying to Active Vista or Server 2008, you might get the following error:
and this is due to the way that both Vista, Server 2008 and Windows 7 handle registration.
For more information on this topic, see Microsoft’s Volume Licensing website.
If you have NOT setup a KMS, but do have a MAK, then a simple work around is to go to:
Control Panel > System > Windows activation and click “Change Product Key”
and enter the key that was provided.
Hope this helps!