Thanks for the clarification.
So did something about your environment change back in May? My suspicion is that, based on '6001: LiveUpdate failed because the LiveUpdate package is corrupt. Internal authentication files are not present.', is that perhaps a firewall, a proxy or some other gateway appliance or application, was put into place or enabled (or possibly even upgraded) that is scanning and modifying the content received from LiveUpdate.
You mentioned that the SSC is 'version 6'. From what I can find, this translates to Symantec Antivirus 9.x. If this is true and this is the version you are using, let me be frank: you are doing the security of your environment no favours by using a product that old--it can't handle the modern threat landscape, and it's not even supported anymore. Definitions are no longer certified for use with SAV 9.x (emphasis mine):
Symantec Antivirus 9.x will reach its End of Standard Support as of March 31, 2009. Virus definition updates for version 9.x will be discontinued on April 1, 2009. Please contact your account manager or reseller for information about our current shipping versions. (http://www.symantec.com/business/security_response/definitions/download/detail.jsp?gid=savce)
sandra