procedure TFormMain.ExportToClick(Sender: TObject);
begin
  ExcelSave.FileName := '';
  if (not CheckExcelRun) and (ExcelSave.Execute) then begin
    ExcelFileName := ExcelSave.FileName;
    CreateExcelFile();
  end
  else begin
      MyExcel := Unassigned;
      Application.MessageBox(
            PWChar('Закройте открытые копии Microsoft Excel!'),
            PWChar('Ошибка'), MB_ICONERROR);
  end;
end;

function CheckExcelRun : boolean;
begin
  try
    MyExcel := GetActiveOleObject(ExcelApp);
    Result := True;
  except
    Result := false;
  end;
end;