Why is there a service event subscription event in 0.6.0.2 for microsoft.com:serviceId:X_MS_MediaReceiverRegistrar for the HPMSC renderer? This event was not generated in 0.5.0.2, and the resulting flow allowed the renderer to successfully connect.
I could see trying all these things - uplevel Java, uninstall MediaSmart Gateway, etc., if I couldn't get any version of serviio to work properly. But the fact that the previous version of serviio is working with the renderer tells me that something was introduced in the new version that breaks the established authorization.
I remember reading somewhere that a compliant renderer device - which the HPMSC is - needs proper authorization from the server to connect. It might possibly be that the HPMSC auth flow that happens when the HPMSC Windows Media Extender connects to the Vista server (which happens before serviio is started) establishes the authorization, then the new uPnp registration event that serviio 0.6.0.2 executes breaks the authorization. Since the Registrar/authorization event isn't done in 0.5.0.2, the renderer effectively "rides on the coattails" of the already established authorization for the device.
I am by no means an expert in windows media streaming...

I work at Hewlett-Packard in software development, but not in this area. And unfortunately the HPMSC development team has long since disbanded. I know there are a lot of HPMSC owners out there that would LOVE to have serviio, it is lightyears ahead of the braindead built-in Windows support. I hope we can figure this out!