SSL VPN Client stop working

I have a RB2011UiAS-RM with RouterOS 6.20 at home and we are using SSL VPN with FortClient in our company.

When i want to connect with my notebook (Lenovo X240, Kubuntu 14.04 LTS) to VPN, the FortiClient established the connection an after a few settings it stops working. It only stops working, the client already says it is connected. It makes no sense if lan or wlan.

At first i thought my notebook is the problem. But when i use other internet connections (3G, at work, parents home, etc.) it works without problems.

For more testing i took the notebook of my girlfriend (windows 7, FortiClient) and there are also no problems connecting to VPN over RouterOS.

What is here the problem? Can anybody help me?