Aircard 762s does not work with VPN via USB

Hi,

I have following problem:

When I create VPN connection my internet stops working after the connection to the VPN serves is established (all traffic dies).

The problem is only present when I connect to the Aircard 762S via USB cable. If I deactivate the direct IP connection via USB and connect to the Aircard via Wi-Fi the VPN connection works.

So the VPN in my mac environment requires certain TCP ports. Do I Have to set any specific port forwarding to the Aircard setting to make the connection work through USB cable? VPN traffic passtrough and all the other 'easy' solution are enabled.

I am running MAC OS X El Capitan.

Thanks you in advance for any suggestions what to try!