Festplattenlaufwerk auswerfen/unmounten

[WorstNightmare]

Delphi-Quellcode:

const
  FILE_READ_ACCESS = 1;

  METHOD_BUFFERED = 0;

  FILE_DEVICE_MASS_STORAGE = $2D;
  IOCTL_STORAGE_BASE = FILE_DEVICE_MASS_STORAGE;

  IOCTL_STORAGE_MEDIA_REMOVAL = $002D4804;

  IOCTL_STORAGE_EJECT_MEDIA = (IOCTL_STORAGE_BASE shl 16) or ($0202 shl 2) or
                              (METHOD_BUFFERED) or (FILE_READ_ACCESS shl 14);
type
  _PREVENT_MEDIA_REMOVAL = packed record
    PreventMediaRemoval: ByteBool;
  end;
  PREVENT_MEDIA_REMOVAL = _PREVENT_MEDIA_REMOVAL;

procedure TestUnmount;
var
  hDisk: THandle;
  written: DWORD;
  PMR: PREVENT_MEDIA_REMOVAL;
begin
  hDisk := CreateFile('\\.\N:', GENERIC_READ or GENERIC_WRITE, FILE_SHARE_READ or FILE_SHARE_WRITE, nil, OPEN_EXISTING, 0, 0);

  if hDisk = INVALID_HANDLE_VALUE then
    raise Exception.Create('opening failed');

  if not LockVolume(hDisk) then
    Showmessage('not locked!!');

  if not DeviceIOControl(hDisk, FSCTL_DISMOUNT_VOLUME, nil, 0, nil, 0, written, nil) then
    Showmessage('dismounting failed');

  PMR.PreventMediaRemoval := False;

  if not DeviceIOControl(hDisk, IOCTL_STORAGE_MEDIA_REMOVAL, @PMR, SizeOf(PMR), nil, 0, written, nil) then
    Showmessage('couldn''t set removal = false');

  if not DeviceIOControl(hDisk, IOCTL_STORAGE_EJECT_MEDIA, nil, 0, nil, 0, written, nil) then
    RaiseLastOSError;

  CloseHandle(hDisk);

Code 1: Unzulässige Funktion.

Was ist denn falsch?