In LW tools > options > advanced > firewall config. Change LW's listening port to 65000 (you can try any other ports in the range of 49152 - 65535) > apply > ok.
You didn't say whether the Speeedstream has UPnP enabled, or port forwarding set up. If you haven't already, try port forwarding. The instructions are here.
Port Forwarding for the Siemens 4200
Don't forget to set up a static IP address first. LW's listening port, port number in the 'manual port forward' box & port forwarded within the Speedstream setup pages should all be the same number.
Did your LW lose connection after you upgraded to a newer version?