This document helps you find out whether your firewall prevents LiveUpdate from downloading updates.
Confirm that the correct ports and protocols are available for LiveUpdate
Make sure that the firewall allows the LiveUpdate executable to connect to the Internet through the correct ports and that the firewall allows connections to the correct domains. Read your firewall's documentation or contact the manufacturer to find out how to confirm these settings.
Note: Symantec does not supply IP addresses for Symantec LiveUpdate servers. The server addresses are not static and, consequently, routing directly to an IP address may cause LiveUpdate to fail.
Download a Livetri.zip file to troubleshoot possible corruption