No VPN connection to Server 2012 R2 possible

Hi,

we have set up a new Server 2012 R2 as HyperV-host. As virtual machines there are running two server 2012 R2, one as Domain controller, one for exchange.
Now we are trying to use vpn with the domain-controller. So we installed the role, activated everything and forwarded in our router ports 1723 (tcp and also udp even that i know this is not used) and GRE. We forwarded them to the IP of the vm (domain controller).

In the event log of this vm i can see warning ID 20209. It tells me that my IP was trying to connect to the vpn server but that there are maybe gre-pakets blocked.
HyperV-Host and VM has no firewall active for testing...

How can i test whats going wrong. Or is it a network problem? inside the LAN i can connect (doesn´t make sense, but i tested). If i ping google.de, i lost 5-20% of my pakets at the moment. The provider is looking for this, but still hasn´t found the problem.
Could this my problem ?

thanks for helping

loosain