Question : Update Panel not loading DropDown

I must be missing something simple here.  I have two drop downs.  The first one, Category, pulls from a DB.  The second should build based on the selected text in the first.

This works fine when I set AutoPostBack to true for the 1st Dropdown.   But I need it to only post back to the 2nd dropdown.  My UpdatePanel is not refreshing though.  I've tried all sorts of triggers and can't get it to go.  Please advise.  Thanks - 
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<cc2:OboutDropDownList ID="ddCategory" runat="server" 
                            DataSourceID="dsCategories" DataValueField="Category" 
                            DataTextField="Category" AppendDataBoundItems="true" 
                            onselectedindexchanged="ddCategory_SelectedIndexChanged">
                            <asp:ListItem></asp:ListItem>
                        </cc2:OboutDropDownList>
                        <asp:SqlDataSource ID="dsCategories" runat="server" 
                            ConnectionString="<%$ ConnectionStrings:SmashHausConnectionString %>"  
                            SelectCommand="SELECT DISTINCT [Category] FROM [Categories]"></asp:SqlDataSource>
                        <asp:RequiredFieldValidator ID="RequiredFieldValidator5" ControlToValidate="ddCategory" InitialValue="" runat="server" ErrorMessage="Category Required">*</asp:RequiredFieldValidator>


                        <asp:UpdatePanel ID="UpdatePanel2" runat="server" UpdateMode="Conditional">
                        <ContentTemplate>
                        <% Response.Write( DateTime.Now.Second.ToString()); %>
                            <cc2:OboutDropDownList ID="ddSubCategory" runat="server" DataSourceID="dsSubCategories" 
                                DataTextField="SubCategory" AppendDataBoundItems="true">
                                <asp:ListItem></asp:ListItem>
                            </cc2:OboutDropDownList>                        
                        </ContentTemplate>
                        <Triggers>
                            <asp:AsyncPostBackTrigger ControlID="ddCategory" EventName="SelectedIndexChanged" />
                            
                        </Triggers>
                        </asp:UpdatePanel>

Answer : Update Panel not loading DropDown

I'm so sorry....
I didn't lock the range. Please see below.

=IF(ISNA(VLOOKUP(A2,$C$1:$D$21,2,FALSE)),"",VLOOKUP(A2,$C$1:$D$21,2,FALSE))
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