Radiobuttonlist selectedindexchanged not firing!

[discusshere]

I am stuck with the Radiobuttonlist not working despite the autopostback="true" . It is strange because it was working well previously. I did not make any change to the code. Here is the code that I am using.

If staple value="5" is checked, it should make the div staplelocation visible.Code behind is also available below.

<table border="true" bordercolor="black">
            <td>
            <asp:RadioButtonList ID="RadioBinding"  runat="server" AutoPostBack="true" RepeatColumns="5" OnSelectedIndexChanged="RadioBinding_SelectedIndexChanged" >
                <asp:ListItem Text="None" Selected="True" Value="1"></asp:ListItem>
                <asp:ListItem Text="3 Hole" Value="2"></asp:ListItem>
                <asp:ListItem Text="Coil(Cost based on # sheets)" Value="3"></asp:ListItem>
                <asp:ListItem Text="Comb(Cost based on # sheets)" Value="4"></asp:ListItem>
                <asp:ListItem Text="Staple" Value="5"></asp:ListItem>
            </asp:RadioButtonList>
            </td>
            </table>
 
            <div id="stapleLocation" runat="server" visible="false">
 
            <br /><br />
            <strong><u>Staple Location:</u></strong>
            <table border="true" bordercolor="black">
            <td>
            <asp:RadioButtonList ID="RadioStapleLoc" runat="server" AutoPostBack="true" RepeatColumns="5" >
                <asp:ListItem Selected="True" Text="Top Left Corner" Value="11"></asp:ListItem>
                <asp:ListItem Text="Staple 1" Value="21"></asp:ListItem>
                <asp:ListItem Text="Staple 2" Value="31"></asp:ListItem>
                <asp:ListItem Text="Staple 3" Value="41"></asp:ListItem>
                <asp:ListItem Text="Staple 4" Value="51"></asp:ListItem>
            </asp:RadioButtonList>
            </td>
            </table>
            </div>
 
 
protected void RadioBinding_SelectedIndexChanged(object sender, EventArgs e)
        {
            //*****************Binding:staple clicked, display staple location*******************//
            if (this.RadioBinding.SelectedValue == "5")
            {
                this.stapleLocation.Visible = true;
            }
            else
            {
                this.stapleLocation.Visible = false;
            }
        }