Hi,
As long you can browse to these websites then there should not be problem
HTTP
liveupdate.symantec.com
liveupdate.symantecliveupdate.com
They use port 80 for downloading defintion
Communication port we use 8014 do telenet from client you can check is there any block.
Title: Which communication ports does Symantec Endpoint Protection use?
Article:TECH163787
Article URL http://www.symantec.com/docs/TECH163787