The VSL house style for Sibelius seems to use a number of fonts which are not necessarily installed on most computers (at least, they're not on mine). In Sibelius 6 and prior, you'd never have known because Sibelius just substitutes the fonts automatically, but in version 7 Sibelius comes up with a "missing fonts" dialog when you open a score that uses the VSL house style.
You can easily override this dialog if it doesn't worry you, but it bugs me to have missing font references and with the aid of a very helpful guy on the Sibelius forum, I've tracked down the culprits. Here's the fix that worked for me:
1. Delete the last four custom symbols, which use text styles "Vivo" and "Maestro (2)": these in turn use the fonts of the same name.
2. Edit the text style "Comment" which currently uses font "Lucida Grande", and edit text style "Version" which uses font "Marker felt".
Of course, other people may get different messages depending on what fonts are installed on their systems.
Mike