Are you running a GUP? This error:
(LU file download failed due to HTTP error:0) points to possible GUP issues.
See -
Troubleshooting the Group Update Provider (GUP) in Symantec Endpoint Protection (SEP)
http://www.symantec.com/business/support/index?page=content&id=TECH104539&actp=search&viewlocale=en_US&searchid=1287594345166
Moving this thread to the Endpoint forum.
Best,
Thomas