sep determine virus definition is missing.
I run live update again, no update. do the needful.
Is your client manage or unmanage
edit
This can due to of definition is corrupted. Remove it wait for update and for unmanage run live update again.
Run this
http://www.symantec.com/business/support/index?page=content&id=TECH102606
What's the exact version of SEP here?
Run the symhelp tool on it to see what shows
About Symantec Help (SymHelp)