The error, in your quote above that I've added emphasis to, is almost always produced by the presence of some third party software running on your networked computers.
My advice would be to Look at the each indivdual machine for firewalls and antivirus security suites (Comodo, Zone Alarm, McAfee, Norton, etc.) uninstall them, get your network up and running and then re-install later. There are of course ways and means of tweaking these applications to permit and allow trusted network nodes into their respective security controlled environment. But if you're not sure how to do this, then uninstalling and reinstalling might help you get the ball moving. Keep us posted.