Using OboutDropDownList inside an ASP updatePanel

I'm facing a problem related with a OboutDropDownList inside an ASP UpdatePanel. I've used the an ASP DropDownList inside an update panel and it works properly:

<asp:UpdatePanel runat="server" UpdateMode="Conditional">
<Triggers>
    <asp:AsyncPostBackTrigger ControlID="ddOne"
        EventName="ddOneEvent" />
    <asp:AsyncPostBackTrigger ControlID="ddTwo"
        EventName="ddTwoEvent" />
</Triggers>
<ContentTemplate>
            <table>
                    <td>
                            <asp:DropDownList ID="ddOne" CssClass="styled-select" runat="server" AutoPostBack="true" AppendDataBoundItems="false" OnSelectedIndexChanged="ddOneEvent" Width="90%">
                                <asp:ListItem Text="Select type" Value="0" />
                                <asp:ListItem Text="Deviation" Value="DEVIATION" />
                                <asp:ListItem Text="Breakpoint" Value="BREAKPOINT" />
                            </asp:DropDownList>
                        </td>
                        <td style="width: 10%">
                            <asp:DropDownList runat="server" ID="ddTwo" DataTextField="TITLE" AutoPostBack="true" OnSelectedIndexChanged="ddTwoEvent" Width="90%">
                                <asp:ListItem Text="Select incidence" Value="0" />
                            </asp:DropDownList>
                        </td>
                    </tr>
                </table>
            </td>
            <td style="width: 50%">
                <cc3:ListBox ID="lbThree" runat="server" DataTextField="Title" Height="120px" Width="90%" AutoPostBack="true">
                </cc3:ListBox>
            </td>
        </tr>
    </table>
</ContentTemplate>

But I have a problem when I change the ASP DropDownList by a OboutDropDownList, like this:

<asp:UpdatePanel runat="server" UpdateMode="Conditional">
<Triggers>
    <asp:AsyncPostBackTrigger ControlID="ddOne"
        EventName="ddOneEvent" />
    <asp:AsyncPostBackTrigger ControlID="ddTwo"
        EventName="ddTwoEvent" />
</Triggers>
<ContentTemplate>
            <table>
                    <td>
                            <obout:OboutDropDownList ID="ddOne" CssClass="styled-select" runat="server" AutoPostBack="true" AppendDataBoundItems="false" OnSelectedIndexChanged="ddOneEvent" Width="90%">
                                <asp:ListItem Text="Select type" Value="0" />
                                <asp:ListItem Text="Deviation" Value="DEVIATION" />
                                <asp:ListItem Text="Breakpoint" Value="BREAKPOINT" />
                            </obout:OboutDropDownList>
                        </td>
                        <td style="width: 10%">
                            <obout:OboutDropDownList runat="server" ID="ddTwo" DataTextField="TITLE" AutoPostBack="true" OnSelectedIndexChanged="ddTwoEvent" Width="90%">
                                <asp:ListItem Text="Select incidence" Value="0" />
                            </obout:OboutDropDownList>
                        </td>
                    </tr>
                </table>
            </td>
            <td style="width: 50%">
                <cc3:ListBox ID="lbThree" runat="server" DataTextField="Title" Height="120px" Width="90%" AutoPostBack="true">
                </cc3:ListBox>
            </td>
        </tr>
    </table>
</ContentTemplate>

In this way, I'm getting the following exception:

0x800a138f - 0x800a138f - JavaScript runtime error: Unable to get property 'id' of undefined or null reference

Could you help me out, please?

Thanks in advance!