MapObjects2.4 出现问题 “未处理COMException” Valid object expected as argument.

private AxMapObjects2.AxMap axMap1;
private void map_Load(object sender, EventArgs e)
        {
            this.Location = new Point(210, 80);
            MapObjects2.DataConnection dc = new MapObjects2 .DataConnectionClass();
            //定义图层
            MapObjects2.MapLayer layer = new MapObjects2.MapLayerClass();
            dc.Database = "" + Application.StartupPath + "";            if (!dc.Connect())//连接不成功就退出
            {
                MessageBox.Show("在指定的文件夹下没找到图层数据文件");
                Application.Exit();
            }            else//连接成功了就加载地图
            {
                //加载图层States，
                  layer.GeoDataset = dc.FindGeoDataset("mas1.bmp");  <--错误指向这句
                axMap1.Layers.Add(layer);
            }
            axMap1.Refresh();
        }高手请 帮忙，谢谢！