What is the error message you are getting if it is return value =4
then follow this article
"Error: LiveUpdate encountered one or more errors. Return code = 4" in LiveUpdate status in Symantec Endpoint Protection Manager
http://service1.symantec.com/SUPPORT/ent-security.nsf/2326c6a13572aeb788257363002b62aa/3b09d4f329acc39fc12573b400341977?OpenDocument
are you using proxy server if yes then make sure you configure proxy in SEPM
"How to setup the Symantec Endpoint Protection Manager to use specific proxy settings for LiveUpdate" at URL:
http://service1.symantec.com/SUPPORT/ent-security.nsf/docid/2007082113383448