SelectedIndexChanged Event for Dropdownlist AJAX

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ASP.NET

Hello,

Thank you for reading. Here is my situation. I have an UpdatePanel and within in I have 2 dropdownlists.   I want to show the second ddlist only when a specific value is chosen in dropdownlist1. I used Javascript/label etc on the selectedIndexChanged event but still does not work. The event gets fired and I stepped thru the code with no problems but it does not render on screen. Code snippet below. All help is wonderfully,gratefully and thankfully appreciated.

Front End

<asp:UpdatePanel ID="updPanel1" runat="server">
            <ContentTemplate>
          <asp:DropDownList ID="ddlTest1" runat="server" AutoPostBack="true" OnSelectedIndexChanged="ddlTest1_IndexChanged">
            <asp:ListItem Value="" Text="Select one"></asp:ListItem>
            <asp:ListItem Value="Matt" Text="Matt"></asp:ListItem>
            <asp:ListItem Value="Robin" Text="Robin"></asp:ListItem>
            </asp:DropDownList>
            <asp:DropDownList ID="ddlTest2" runat="server" style="visibility:hidden;display:none;">
            <asp:ListItem Text="Select One" Value=""></asp:ListItem>
            <asp:ListItem Text="Tom" Value="Tom"></asp:ListItem>
            <asp:ListItem Text="John" Value="John"></asp:ListItem>
            
      </asp:DropDownList>
</ContentTemplate>
            </asp:UpdatePanel>

And the Codebehind is as follows:

Protected Sub ddlTest1_IndexChanged(ByVal sender As Object, ByVal e As EventArgs)
            If ddlTest1.SelectedValue = "Robin" Then

                  Dim script As String = "<script type='text/javascript'>var elem=document.getElementById('" & Me.ddlTest2.ClientID & "');elem.style.visibility='visible';elem.style.display='block';</script>
          
Page.ClientScript.RegisterClientScriptBlock(Me.GetType(), "newKeyVal", script, True)
                  
            Else
                  Dim script As String = "<script type='text/javascript'>var elem=document.getElementById('" & Me.ddlTest2.ClientID & "');elem.style.visibility='hidden';elem.style.display='block';</script>"
                  Page.ClientScript.RegisterClientScriptBlock(Me.GetType (), "newKeyVal", script, True)
                  
            End If

      End Sub