Problems with connecting to RDP over VPN

Hello

I'm using Windows server 2012 R2 standard, the server is located on an ESXI 6.0.

I did a migration of SBS2008 to Windows Server 2012 with this manual https://blogs.technet.microsoft.com/canitpro/2014/05/27/step-by-step-active-directory-migration-from-windows-server-2008-r2-to-windows-server-2012-r2/

I'm able to setup a PPTP VPN connection to the new server. I'm able to ping to the new server and to the old server aswell, when I'm connected via VPN. But when I want to go to the shares it doesn't work. (Can't find server on IP address) Also the remote desktop doesn't work via VPN. 

I'm able to connect to the old server via RDP and file shares are reachable. I already disabled firewall and endpoint security, still that doesn't seem to resolve the problem.

[Edit]

I narrowed my problem down to the following:

I tracert to the server over the VPN and i get 2 replies:

When I try to RDP to .251 it doesn't work over VPN, but when I try to RDP to the .117 it does work. And that is the new RDP server.
In other words it is possible to make a RDP connection to the internal interface (the one I see in Routing and remote access), but it doesn't work to the Ethernet0 (with IP address .251)

RDP to the old server works over VPN. But I think the problem is something with the Routing and Remote Access, but I got no idea how to solve it.

If there are other things you need, just ask

Thanks for the feedback

Kind regards