Good catch, that NavInstall.
Is this just a variable needed to decide if a mail must be sent to tell that Symantec Antivirus is not installed?
I get the impression you could make it a KiX variable
Code:

Dim $NavInstall
...
$NavInstall = 0   ; no SET
...
    If $NavInstall = 2
      SHELL '@LSERVER\NETLOGON\Admin\postie\postie.exe -host:MAILSERVER -from:it@mydomain.com -to:it@mydomain.com -s:"%COMPUTERNAME% does" +
      " not have Symantec Anti Virus Installed" -nomsg'
    Endif