You cannot enable that, it means You have a mangement sever set somewhere; may be you go this package from your college or from your IT office.
when you receive this package it will have set of rules configured and you wont be able to edit it.
if you want to delete this scan
start
run
type regedit.exe
HKEY_LOCAL_MACHINE\SOFTWARE\Symantec\Symantec Endpoint Protection\AV\LocalScans
Every alphaneumaric folder you see there is a scan setting.
You can check if there are any unwanted scans saved in registry and remove them if needed.
https://www-secure.symantec.com/connect/forums/scan-log-shows-multiple-old-scans-still-running