That doesn't seem to do quite the same thing. GetAttributes() tells me that neither C:/Windows/System32 nor many of the files in it are READONLY. Yet, I can't write to that directory, or to any of the files in it.
Re^4: Inline.pm and untainting
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GetAttributes() (from Win32::File) returns the file attributes that were invented around 1980 for MS-DOS, namely ARCHIVE, DIRECTORY, HIDDEN, READONLY, and SYSTEM, plus three new using the remaining bits of a byte, invented somewhere around Windows 98 or NT 4.0: OFFLINE, COMPRESSED, and TEMPORARY. Again, these attributes do not have any relation to the ACLs. Win32::Security::ACL should be able to access the ACLs and to tell you why you can't write to the directory.
Today I will gladly share my knowledge and experience, for there are no sweeter words than "I told you so". ;-)