Dropdown List Selected Index Changed - Compiler Didn't See The Code

I did my drop down list that get it,s values from database and when run the application it did not work and compiler did not see the code

// aspx
<asp:UpdatePanel ID="UpdatePanel3" runat="server">
<ContentTemplate>
<asp:DropDownList ID="DDlProductFamily" runat="server"
ondatabound="DDlProductFamily_DataBound"
onselectedindexchanged="DDlProductFamily_SelectedIndexChanged">
</asp:DropDownList>
</ContentTemplate>
<Triggers>
<asp:AsyncPostBackTrigger ControlID="DDlProductFamily" EventName="SelectedIndexChanged" />
</Triggers>
</asp:UpdatePanel>
// cs
protected void DDlProductFamily_SelectedIndexChanged(object sender, EventArgs e)
{
using (SqlConnection Con = Connection.GetConnection())
{
SqlCommand Com = new SqlCommand("SelectThumbByProductFamily", Con);
Com.CommandType = CommandType.StoredProcedure;
Com.Parameters.Add(Parameter.NewInt("@ProductCategory_Id",
DDlProductFamily.SelectedValue.ToString()));
SqlDataAdapter DA = new SqlDataAdapter(Com);
DA.Fill(dt);
DataList1.DataSource = dt;
DataList1.DataBind();
}
}