You seek to prevent a realtime filesystem antivirus product from scanning the temporary folder Symantec Scan Engine uses for scanning.
By default, the temporary scanning folder for Scan Engine on Windows (32 bit) is C:\Program Files\Symantec\Scan Engine\Temp.
By default, the temporary scanning folder for Scan Engine on Windows (64 bit) is C:\Program Files (x86)\Symantec\Scan Engine\Temp.
By default, the temporary scanning folder for Scan Engine on Linux or Solaris is /opt/Symantec/Symantec Scan Engine/Temp.
NOTE:
Assuming that you also have a local antivirus scanner on other clients in the network, the following document is of interest to you:
'Symantec Scan Engine scan errors while trying to scan files across a network path or drives'
http://www.symantec.com/docs/TECH90466