Setting file permissions

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scripting

In a custom action of the setup, a VB Script is run to perform several actions. i also want to set permissions on file "abc.def" such that only "Local System" (S-1-5-18) can access it. I tried to find out how to do that with cacls:

cacls abc.def /G SID#S-1-5-18:F

But that command results in the error message "No mapping between account names and security IDs was done" when I try it from a commandline in the folder of that file (administrative user, elevated rights).
How can that be achieved (please note: must work on XP and Win7 and corresponding server OS)?