datalist绑定滚动图片问题？

我的代码如下： 
<div id="demo" style="overflow: hidden; width: 685px">
                            <table>
                                <tr>
                                    <td id="demo1">
                                        <asp:DataList ID="DataList1" runat="server" RepeatDirection="Horizontal">
                                            <ItemTemplate>
                                                <asp:Image ID="Image7" runat="server" ImageUrl='<%# Eval("imge") %>'></asp:Image>&nbsp;
                                            </ItemTemplate>
                                        </asp:DataList></td>
                                    <td id="demo2">
                                    </td>
                                </tr>
                            </table>
                        </div>                        <script type="text/javascript"> 
var speed=3 
demo2.innerHTML=demo1.innerHTML 
function Marquee(){ 
if(demo2.offsetWidth-demo.scrollLeft<=0) 
demo.scrollLeft-=demo1.offsetWidth 
else{ 
demo.scrollLeft++
} 
} 
var MyMar=setInterval(Marquee,speed) 
demo.onmouseover=function() {clearInterval(MyMar)} 
demo.onmouseout=function() {MyMar=setInterval(Marquee,speed)} 
                        </script>
他是实现了无缝滚动 但是就只滚动了一次是什么原因啊？
各位帮帮忙啊! 谢谢了先