Can't Execute Sql In Code-behind

 I found a example of using a button inside of a gridview at http://msdn2.microsoft.com/en-us/library/system.web.ui.webcontrols.buttonfield.aspx.
I modified the code-behind and added:
      // Insert the producer into the database
      SqlDataSource sds = selectedRow.FindControl("sqlItemInsertIntoListing") as SqlDataSource;
      sds.Insert();

but the page throws an error.
Can someone look at my code-behind and show me how to execute the line 56 in the code-behind?  Thanks. 
 


Object reference not set to an instance of an object.



Description: An
unhandled exception occurred during the execution of the current web
request. Please review the stack trace for more information about the
error and where it originated in the code.



Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.



Source Error:






Line 55: // Insert the producer into the database
Line 56: SqlDataSource sds = selectedRow.FindControl("sqlItemInsertIntoListing") as SqlDataSource;
Line 57: sds.Insert();
Line 58:
Line 59: } 
Below is my code:
 ASPX PAGE:
    <asp:Label ID="Message" ForeColor="Red" runat="server" AssociatedControlID="CustomersGridView" />
    <!-- Populate the Columns collection declaratively. -->
    <asp:GridView ID="CustomersGridView" DataSourceID="CustomersSqlDataSource" DataKeyNames="ItemID"
        AutoGenerateColumns="False" OnRowCommand="CustomersGridView_RowCommand"
        runat="server" AllowPaging="True" AllowSorting="True" PageSize="50">
        <Columns>
            <asp:BoundField DataField="ProducerName" HeaderText="Producer" SortExpression="ProducerName" />
            <asp:BoundField DataField="ItemName" HeaderText="Item" SortExpression="ItemName" />
            <asp:BoundField DataField="Year" HeaderText="Year" SortExpression="Year" />
            <asp:BoundField DataField="RegionMasterName" HeaderText="Region" SortExpression="RegionMasterName" />
            <asp:BoundField DataField="CountryName" HeaderText="Country" SortExpression="CountryName" />
            <asp:BoundField DataField="StateName" HeaderText="State" SortExpression="StateName" />
            <asp:TemplateField HeaderText="ItemID" InsertVisible="False" Visible="false" SortExpression="ItemID">
                <ItemTemplate>
                    <asp:Label ID="ItemID" runat="server" Text='<%# Bind("ItemID") %>' Visible="false"></asp:Label>
                    <asp:SqlDataSource ID="sqlItemInsertIntoPart" runat="server" ConnectionString="<%$ ConnectionStrings:VBJimboConn %>"
                        InsertCommand="INSERT INTO [ZCPart] ([PartUserId], [PartItemID]) VALUES (@PartUserId, @PartItemID)" OnInserting="sqlItemInsertIntoPart_Inserting" >
                        <InsertParameters>
                            <asp:Parameter Name="PartUserId" />
                            <asp:ControlParameter Name="PartItemID" ControlID="ItemID" PropertyName="Text" Type="Int32" />
                        </InsertParameters>
                    </asp:SqlDataSource>
                </ItemTemplate>
            </asp:TemplateField>
            <asp:ButtonField ButtonType="Button" CommandName="Select"
                Text="Add to Part" Visible="True" />
            <asp:HyperLinkField DataNavigateUrlFields="ItemID"
                DataNavigateUrlFormatString="ItemDetails.aspx?ItemID={0}" Text="Details" />
        </Columns>
    </asp:GridView>

        <asp:SqlDataSource ID="CustomersSqlDataSource" runat="server" ConnectionString="<%$ ConnectionStrings:CONNSTG %>"....>
        </asp:SqlDataSource>

 
CODE-BEHIND:
using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;

partial class Inventory_InventoryList : System.Web.UI.Page
{

    protected void Page_Load(object sender, System.EventArgs e)
    {
        if (!Page.IsPostBack)
        {
            if (!User.Identity.IsAuthenticated)
            {
                CustomersGridView.Columns[CustomersGridView.Columns.Count - 2].Visible = false;
            }
        }
    }
    protected void sqlItemInsertIntoPart_Inserting(object sender, System.Web.UI.WebControls.SqlDataSourceCommandEventArgs e)
    {
        e.Command.Parameters["@PartUserId"].Value = Membership.GetUser().ProviderUserKey;
    }


// Source for gvInventoryList to display message: http://msdn2.microsoft.com/en-us/library/system.web.ui.webcontrols.buttonfield.aspx
  protected void CustomersGridView_RowCommand(Object sender, GridViewCommandEventArgs e)
  {

    // If multiple ButtonField column fields are used, use the
    // CommandName property to determine which button was clicked.
    if(e.CommandName=="Select")
    {

      // Convert the row index stored in the CommandArgument
      // property to an Integer.
      int index = Convert.ToInt32(e.CommandArgument);   

      // Get the last name of the selected author from the appropriate
      // cell in the GridView control.
      GridViewRow selectedRow = CustomersGridView.Rows[index];
      TableCell contactName = selectedRow.Cells[1];
      string contact = contactName.Text; 

      // Display the selected author.
      Message.Text = "You selected " + contact + ".";
     
      // Insert the producer into the database
      SqlDataSource sds = selectedRow.FindControl("sqlItemInsertIntoListing") as SqlDataSource;
      sds.Insert();

    }

  }

}