How are you getting the template installer?

Unlocked copies of WD7 will show the download link under Help>Download templates
Trial versions will not.

If this is how you are getting the installer, then obviously there's a problem because without an unlocked copy you wouldn't even be able to get the installer in the first place.

Open a ticket with xara at support.xara.com

If you are getting the installer by some other means, then you might be trying to install the templates for the wrong version. (for example you say you installed WD7 but the error message mentions WD7 'Premium')