Problem with pfSense OpenVPN behind BinTEC-firewall

[mikbo]

Hi,
we are trying to setup an OpenVPN server on a pfSense 2.0.1 box which is behind a BinTEC firewall. The problem: after the connection the client has only access to the pfSense firewall but couldn´t reach any other device on the network. But when we change the default gateway of a device on the network away from the BinTEC to the pfSense the device and the connected OpenVPN client can connect to each other. First we thought of a routing problem but when we add the pfSense box as a static route to the OpenVPN network on the BinTEC the clients are no longer able to reach the OpenVPN server on the pfSense box.
Does anybody has any hints what is going wrong?

Greetings,

Mike