You need to uninstall and reinstall Symantec LiveUpdate.
Missing or corrupt LiveUpdate
Use Add or Remove Programs in the Control Panel to uninstall LiveUpdate. Download and run the LiveUpdate installer to install LiveUpdate again.
To uninstall and reinstall LiveUpdate
NOTE: If Symantec Mail Security for Microsoft Exchange is installed, be sure to register it with LiveUpdate as per http://www.symantec.com/docs/TECH81935