I really need some help. I've spent the past two hours trying to figure this out... and I can't. I don't know what I'm doing wrong.

This is on my Default.aspx page:

<asp:DropDownList ID="ddlMagazineList" runat="server" DataSourceID="MagazinesDataSource" OnSelectedIndexChanged="updateKey(this.value);"
    DataTextField="Name" DataValueField="Id">
</asp:DropDownList><asp:SqlDataSource ID="MagazinesDataSource" runat="server" ConnectionString="<%$ ConnectionStrings:ConnectionString %>"
    SelectCommand="Get_Magazine_List" SelectCommandType="StoredProcedure"></asp:SqlDataSource>
<asp:Panel ID="panel1" style='width:100px; height:100px' BorderWidth='1' runat='server'>
</asp:Panel>
<ajaxToolkit:DynamicPopulateExtender ID="dp1" runat="server"
    TargetControlID="panel1"
    ClearContentsDuringUpdate="true"
    ServiceMethod="GetHtml"
    UpdatingCssClass="dynamicPopulate_Updating" />

On the code behind, I have the following:

...
using System.Web.Services;
using System.Web.Script.Services;
using System.IO;
using AjaxControlToolkit;
...

public partial class _Default : System.Web.UI.Page
{
[WebMethod]
    public string GetHtml(string contextKey)
    {
        System.Threading.Thread.Sleep(1000);
        string html = GetProducts(Convert.ToInt32(contextKey));
        return html;
    }
    private string GetProducts(int categoryID)
    {
        string connectionString = "Server=localhost;Database=Northwind;Trusted_Connection=true";
        SqlConnection myConnection = new SqlConnection(connectionString);
        SqlCommand myCommand = new SqlCommand("SELECT ProductID, ProductName FROM Products WHERE CategoryID = @CategoryID", myConnection);
        myCommand.Parameters.AddWithValue("@CategoryID", categoryID);
        SqlDataAdapter ad = new SqlDataAdapter(myCommand);
        DataSet ds = new DataSet();
        ad.Fill(ds);
        GridView gv = new GridView();
        gv.ID = "GridView1";
        gv.DataSource = ds;
        gv.DataBind();
        StringWriter sw = new StringWriter();
        HtmlTextWriter htw = new HtmlTextWriter(sw);
        gv.RenderControl(htw);
        htw.Close();
        return sw.ToString();
    }
}

Running that, I get the error CS1026: ) expected in regards to the OnSelectedIndexChanged="updateKey(this.value);"

I've also tried removing that from the DropDownList and changing the DynamicPopulateExtender to:

<ajaxToolkit:DynamicPopulateExtender ID="dp1" runat="server"
    TargetControlID="panel1"
    PopulateTriggerControlID="ddlMagazineList"
    ClearContentsDuringUpdate="true"
    ServiceMethod="GetHtml"
    UpdatingCssClass="dynamicPopulate_Updating" />

This doesn't give a .NET error, but when you select something it returns "Web Service call failed: 500."

In my opinion, that is a horrible error for me... as I have no idea WHY it failed.  

I really don't know... if someone could point me in the right direction I would really, truly appreciate it! Thank you!

Sincerely,
Andrew Tatum