DDSmoothmenu不使用键盘（箭头键）

Question

ddsmoothmenu无法使用键盘上的箭头键。

当li列表太长时，它会低于页面，因此无法点击li。那么我该如何处理这个问题呢？

 ddsmoothmenu.init({
            mainmenuid: "divMenu", //menu DIV id
            orientation: 'h', //Horizontal or vertical menu: Set to "h" or "v"
            classname: 'ddsmoothmenu', //class added to menu's outer DIV            
            contentsource: "markup" //"markup" or ["container_id", "path_to_menu_file"]
        })


<div align="left" id="tdmenu">
    <table cellpadding="0" cellspacing="0" border="0" width="100%">
        <tr>
            <td width="75%">
                <div id="divMenu" class="ddsmoothmenu">
                    <ul>
                        <li>
                            <a href="javascript:showHome();">Home</a>
                        </li>
                        <asp:Literal runat="server" ID="ltMenu"></asp:Literal>
                        <li runat="server" id="divProSupportTicket" visible="false">
                            <a href="javascript:showWindow('supportticket.aspx',900,600,100)">
                                <img src="images/support.png" alt="Software Support Form" height="20" title="Software Support Form" />
                            </a>
                        </li>
                        <li>
                            <div id="HelpIcon" style="border: solid 1px gray; background-color: #4C83F8; border-radius: 50%; cursor: pointer; width: 25px; margin-left: 10px; margin-top: 2px;" title="Help Information" onclick="showHelp('home_Vehicle');">
                                <span style="font-size: 20px; color: White; font-weight: bold; padding: 0px 7px 0px 7px;">
                                    <i>i</i> 
                                </span>
                            </div>
                        </li>
                        <li runat="server" id="liCompanyContacts" visible="false"></li>
                    </ul>
                </div>
            </td>
        </tr>
    </table>
</div>