Server 2012 / Routing and RAS with PPTP VPN / cannot ping from client to Internal NIC of RAS Server

Hello together, 

having the following problem: 

Server 2012; acutally patched with single nic and routing and ras service active for pptp vpn connection;

i can connect without any problems via pptp from an client;

i can ping and connect to ever *other* server than to the RAS Server;

i can not ping and connect to the RAS Server it selfs NIC IP adress

i can ping to the RAS Servers Dynamic "RAS (Dial In) Interface".

But i need to get an connection to the normal internal ip 

any ideas about this ? 

thanks 

best

Martin