Drag & drop files using an IDataObject

Hi. I want that my application to allow files dropped from Explorer in a Virtual Treeview (of Mike Lischke, latest version).

The VTV has an event which provides me an IDataObject with the information. I followed the docs from MSDN on what to do with it and came out with this code, but I get an access violation. (on the row marked with !!!!).

Any ideas how to fix it ? Thx.

procedure TfrmMain.vsDragDrop(Sender: TBaseVirtualTree; Source: TObject;
  DataObject: IDataObject; Formats: TFormatArray; Shift: TShiftState;
  Pt: TPoint; var Effect: Integer; Mode: TDropMode);
var medium:TStgMedium;
    EnumFormat:IEnumFormatEtc;
    format:TFormatEtc;
    i, Fetched: integer;
    buffer:array[0..100] of char;
    name: pchar;
    drop:Hdrop;
    nfiles:UInt;
    szFilename: pAnsiChar;
begin
  if DataObject <> nil then
    if succeeded(DataObject.EnumFormatEtc(DATADIR_GET, EnumFormat)) then
      begin
        EnumFormat.Reset;
        while EnumFormat.Next(1, Format, @Fetched) = S_OK do
          begin
           GetClipboardFormatName(format.cfFormat, buffer, 100);
           if buffer = 'FileName' then
           begin
              DataObject.GetData(format, Medium);
              drop := hdrop(GlobalLock(Medium.hGlobal));
              if drop <> 0 then
              begin
                nfiles := dragQueryFile(drop, $FFFFFFFF, szFilename, 255); //!!!!!
                 for i:= 0 to nfiles-1 do
                   begin
                      getmem(szfilename, MAX_PATH+1);
                      zeromemory(szfilename, MAX_PATH);
                      DragQueryFile(drop, i, szfilename, MAX_PATH);
                      showmessage(szFilename);
                   end;
                 GlobalUnlock(medium.hGlobal);
              end;
             ReleaseStgMedium(Medium);
           end;
          end;

     end;

end;