Determine write-access to a directory

I am trying to determine the write-access to a windows-directory, using the method %File.Writeable(). But, this method always returns the boolean "true", even when I have revoked the write-access of Healthshare-user in this directory.

Note:
1) When the same ensemble-service tries to write a file in this directory (which it says is "writeable"), it fails.
2) The method %File.Writeable(...) works perfectly in the case of files.

Any help is appreciated.
Thanks in advance... :-)