I'm getting the "Disconnected from Ironclad Online" message as well. I'm running a basic windows firewall, and it shows Sins as having an exception. I have the newest version of the original Sins (not Entrenchment) running on XP pro edition. I saw on the Stardock forums that certain ports - 6000 and 7000 - needed to be open, and tried opening them under Firewall -> Exceptions -> Add port. No luck.
Is there something else I need to fix? If not, is it possible there is a network firewall in addition to the windows firewall, and this firewall is causing problems? (I'm on a college campus, using their network).