Are you on a windows shared, vps or dedicated?
Usually for shared (not sure about vps/dedicated) I know there are :
Plesk IIS User(IUSR_myname) = is an anonymous access account which used by IIS to access pages on the site for incoming requests
.
Plesk IIS WP User(IWPD_266(myname)) = This is the ASP.NET "user" when using ASP.NET
Plesk Domain User (myname) = is your user you login as accessing the account in Plesk or by FTP.
Not sure what adminstrator / system are, unless you are on vps/dedicated and its specific to that, or permission setup on shared windows has changed.
If you are on shared window hosting, the acount would not be able to run executables (far as I know) as this is disabled for security/stability concerns. If on VPS / Dedicated, you may need to contact support via support.lunarpages.com or
support@lunarpages.com