循环滚动条javascript脚本，遇到多表嵌套时候的问题

这个滚动脚本 遇到多个表嵌套的时候 滚动一次就停止了  
帮忙看看：<table><tr><td>
<table>
<tr><td >a a a </td><td><div id="marquees" align="center" style="width:200; height:100" >
<!-- 这里可以放置数据库操作代码． -->
xxxxxxx
<br>
</div>
</td>
</tr>
</table>
</td></tr>
</table><script language="JavaScript">
marqueesHeight=100;
marqueesWidth=200;
stopscroll=false;with(marquees){
    style.width=200;
    style.height=marqueesHeight;
    style.overflowX="visible";
    style.overflowY="hidden";
    noWrap=true;
    onmouseover=new Function("stopscroll=true");
    onmouseout=new Function("stopscroll=false");
}
document.write('<div id="templayer" style="position:absolute;z-index:1;visibility:hidden"></div>');preTop=0; currentTop=0; function init(){
    templayer.innerHTML="";
    while(templayer.offsetHeight<=marqueesHeight){
      templayer.innerHTML+=marquees.innerHTML;
    }
    marquees.innerHTML=templayer.innerHTML+templayer.innerHTML;
    setInterval("scrollUp()",20);//越大越慢
}
document.body.onload=init;function scrollUp(){
    if(stopscroll==true) return;
    preTop=marquees.scrollTop;
    marquees.scrollTop+=1;
    if(preTop==marquees.scrollTop){
      marquees.scrollTop=templayer.offsetHeight-marqueesHeight;
      marquees.scrollTop+=1;
    }
}
</script>