It is very useful to be able to use HyperV management tools remotely but getting it to work is another matter. I have sucessfully made this work after some experimentation.
1. Make sure server and client are set up to manage and be managed - checking the remote management works on a lan connection first is the best bet.
2. The key to this is authentication - on the remote client (in this case my laptop) - you must be logged on as a user that has administrative rights on the HyperV server - or in the domain if it is a domain menber. You do not necessarily have to be logged onto the domain but the username/password must be recognised.
3. The VPN connection must be logged onto the RRAS server as the same user with administrative rights - so the HyperV server does not get confused.
It took me a while to discover this but it does work - I have just been using it on a clients HyperV core server that needed some adjustments made to the VM settings.