Do you have an external modem?
Try changing ports. In LW tools > options > advanced > firewall config. Change LW's listening port to 64049 (or try other ports in the range of 49152 - 65535) > Apply > ok.
It looks like SITCO also offer a firewall.
SITCO - Services
Any chance that their firewall's part of your internet package? Just have a check to see about that.