Hello,
Does this happen on All Microsoft Updates on Windows 7 Machines??
Was the Windows 7 Firewall Turned off after you had the Symantec Network Threat Protection Installed??
You can disable Windows Firewall after installing Symantec firewall as installing two firewalls may cause potential network access issue.
In fact, during the installation of SEP, Windows Firewall should be disabled.
You can check the following Article:
Windows Firewall is still enabled after installing Symantec Endpoint Protection 11.
http://www.symantec.com/docs/TECH91865
About Windows Firewall and Symantec Endpoint Protection's NTP
Again, after the Microsoft updates you need to Restart the machine.
Hope that helps!!