This article describes how to disable definition shadowing if it has been enabled, and how to enable LiveUpdate in Symantec Scan Engine.
Disable definition shadowing of another Symantec product
For Windows the default location is C:\Program Files\Symantec\Scan Engine\Definitions\AntiVirus
For Linux and Solaris the default location is /opt/SYMCScan/bin/definitions/Antivirus/
Enable LiveUpdate in Symantec Scan Engine