It's the firewall most likely. Check the traffic log to see what it shows. Use this article as a guide as well:
Troubleshoot blocked network traffic due to the Endpoint Protection firewall
Hi,
I would suggest to review firewall policy, by default SEP firewall shoudn't block this feature evern after an upgrade.
Hello,
Did you migrate from 12.1.1101.401 RU1 MP1 to 12.1.6?
Is that 12.1.6 OR 12.1.6 RU1 OR 12.1.6 RU2?
Check the Firewall Rules and check this Article:
http://www.symantec.com/docs/HOWTO80724
Hope that helps!!