Can you post the Actionscript you’re actually trying to use?
The BESClient runs as LocalSystem and the commands are elevated by default, so it should work as long as you don’t have an explicit ‘Deny’ ACL on the file affecting the LocalSystem account.
What I think is more likely is 32-bit redirection. By default the BESClient process runs in 32-bit mode, so you’ll need ‘
action uses wow64 redirection false’ in the ActionScript to run in 64-bit mode; otherwise you’ve actually be affecting \windows\syswow64 instead of the intended \windows\system32 folder.