with WP Piwik Network Activated it seems that there isn't a site being created once you add a new one in the Multisite Network Admin.
The error message in the child-blog (subdomain) is:
Piwik error: The requested website id = 0 couldn't be found
Visiting the frontpage of the newly created site in logged in and logged out browsers doesn't seem to help either, neither does retroperspectively adding the site title change anything - the site doesn't seem to exist as far as Piwik is concerned.
Any kind of ideas on how to resolve that, short of deleting the site and recreating it?