css布局总是发生错位现象，该如何解决？？谢谢！！急！！
效果如下面链接中的图片：
http://tttycleaner.com/1.gif

三行三列的图片总是不能保持三行三列，总是发生错位，麻烦大家该如何解决呢？？
是因为什么导致这个问题呢？？


css文件：
#ttty_content2{
width:774px;
/*height:230px;*/
margin:0px;
background:#FFF;
padding:0px;
border-left:1px   solid   #360;
border-right:1px   solid   #360;
}

#ttty_content2_left{                                       /*第二块内容－－左部显示*/
float:left;
clear:right;
/*width:29%;*/
width:223px;
/*height:220px;*/
margin:0px;
background:#FFF;
padding:0px;
border-right:1px   solid   #360;
}

#ttty_content2_middle{                                     /*第二块内容－－中部显示*/
float:left;
width:45%;
/*width:350px;*/
/*height:450px;*/
margin:0px;
padding:0px;
border-right:1px   solid   #360;
}

#ttty_content2_right{                                     /*第二块内容－－右部显示*/
float:left;
clear:right;
/*width:23%;*/
width:200px;
/*height:200px;*/
margin:0px;
padding:0px;
}


html文件：
<div   id= "ttty_content2_middle ">
<span   class= "ttty_content1_at "> <span   class= "ttty_content2_jptj "> </span> </span>
<ul>
<li> <img   src= "jingpin_img/1.gif "   width= "100 "   height= "100 "   border= "1 "   alt= "移动垃圾桶 "   /> </a> </li>
<li> <img   src= "jingpin_img/2.gif "   width= "100 "   height= "100 "   border= "1 "   alt= "移动垃圾桶 "   /> </a> </li>
<li> <img   src= "jingpin_img/3.gif "   width= "100 "   height= "100 "   border= "1 "   alt= "移动垃圾桶 "   /> </a> </li>
<li> <img   src= "jingpin_img/4.gif "   width= "100 "   height= "100 "   border= "1 "   alt= "垃圾屋 "   /> </a> </li>
<li> <img   src= "jingpin_img/5.gif "   width= "100 "   height= "100 "   border= "1 "   alt= "垃圾屋 "   /> </a> </li>
<li> <img   src= "jingpin_img/6.gif "   width= "100 "   height= "100 "   border= "1 "   alt= "垃圾屋 "   /> </a> </li>
<li> <img   src= "jingpin_img/7.gif "   width= "100 "   height= "100 "   border= "1 "   alt= "保洁三轮车 "   /> </a> </li>
<li> <img   src= "jingpin_img/8.gif "   width= "100 "   height= "100 "   border= "1 "   alt= "保洁三轮车 "   /> </a> </li>
<li> <img   src= "jingpin_img/9.gif "   width= "100 "   height= "100 "   border= "1 "   alt= "保洁三轮车 "   /> </a> </li>
<li> <img   src=