nested datagrid - fejl

Hey

Når jeg forsøger at neste et DataGrid med et andet, får jeg flg. fejl:

System.InvalidCastException: Specified cast is not valid

og min stack trace (som jeg ikke fatter):

[InvalidCastException: Specified cast is not valid.]
  emotor.builder.filearchive.filearchieve_viewFiles.showFiles(Object sender, DataGridItemEventArgs e) +88
  System.Web.UI.WebControls.DataGrid.OnItemDataBound(DataGridItemEventArgs e) +110
  System.Web.UI.WebControls.DataGrid.CreateItem(Int32 itemIndex, Int32 dataSourceIndex, ListItemType itemType, Boolean dataBind, Object dataItem, DataGridColumn[] columns, TableRowCollection rows, PagedDataSource pagedDataSource) +181
  System.Web.UI.WebControls.DataGrid.CreateControlHierarchy(Boolean useDataSource) +1408
  System.Web.UI.WebControls.BaseDataList.OnDataBinding(EventArgs e) +49
  System.Web.UI.WebControls.BaseDataList.DataBind() +23
  emotor.builder.filearchive.filearchieve_viewFiles.showFolders() +250
  emotor.builder.filearchive.filearchieve_viewFiles.Page_Load(Object sender, EventArgs e) +58
  System.Web.UI.Control.OnLoad(EventArgs e) +67
  System.Web.UI.Control.LoadRecursive() +29
  System.Web.UI.Page.ProcessRequestMain() +724


Mine funktion ser ud som følger:

    // Show fake folders (Master DataGrid)
    protected void showFolders() {
      // Set SQL Query
      SqlString = "SELECT folders.id AS sqlMasterID, folders.folderName FROM folders ORDER BY folders.folderName";
      SqlStringDetails = "SELECT filearchive.id AS sqlDetailID, filearchive.fileName, filearchive.folderID FROM filearchive ORDER BY filearchive.fileName";

      // Create and fill Master/Details DataAdapter objects
      CoreLab.MySql.MySqlConnection Conn = OpenMySqlConnection();
      Conn.Open();
      // Master
      CoreLab.MySql.MySqlDataAdapter objAdapterMaster = new CoreLab.MySql.MySqlDataAdapter(SqlString, Conn);
      // Detail
      CoreLab.MySql.MySqlDataAdapter objAdapterDetail = new CoreLab.MySql.MySqlDataAdapter(SqlStringDetails, Conn);
      Conn.Close();

      objAdapterMaster.Fill(ds,"Master");
      objAdapterDetail.Fill(ds,"Detail");

      dg.DataSource = ds.Tables["Master"];
      dg.DataBind();
    }

   
    // Show files (Detail DataGrid)
    protected void showFiles(object sender, DataGridItemEventArgs e) {
      if (e.Item.ItemType == ListItemType.Item || e.Item.ItemType == ListItemType.AlternatingItem) {
        // Build new DataGrid
        DataGrid dgDetails = new DataGrid();

        // Get Master ID
        //int masterID = e.Item.DataItem("sqlMasterID");
        int masterID = Int32.Parse(((System.Data.Common.DbDataRecord)e.Item.DataItem)["sqlMasterID"].ToString());
             
        // Create a DataView
        DataView dv = new DataView();
        dv = ds.Tables["Detail"].DefaultView;
        dv.RowFilter = "sqlMasterID=" + masterID;

        // Bind the data to the new DataGrid
        dgDetails.DataSource = dv;
        dgDetails.DataBind();

        // Add the DataGrid to the second column
        e.Item.Cells[1].Controls.Add(dgDetails);
      }
    }

og min webform:

<asp:DataGrid id=dg runat="server" AutoGenerateColumns="False" ShowHeader="False" OnItemDataBound="showFiles">
  <Columns>
    <asp:TemplateColumn HeaderText="mapper">
      <ItemTemplate><%#DataBinder.Eval(Container, "DataItem.folderName")%></ItemTemplate>
    </asp:TemplateColumn>
    <asp:TemplateColumn HeaderText="filer">
      <ItemTemplate>

      </ItemTemplate>
    </asp:TemplateColumn>
  </Columns>
</asp:DataGrid>

Nogle der kan hjælpe?