If you run the windows firewall and zonealarm within the same windows session your connection will be destabilised (I had this problem running a server behind both on a non-standard port, I could not see the server but the machine otherwise appeared connected, I uninstalled zonealarm, rebooted, problem gone...). This might be the issue? Spybot should not be necessary while playing sfc, so why not turn it off, free up the resources and eliminate it as the culprit?