Jscript移动图片报错

界面程序
       <%
String newAddress="";
String newAddress_small="";
String[] address=(String[])request.getAttribute("address");
String[] address_small=(String[])request.getAttribute("address_small");
for(int i=0;i<address.length;i++){
newAddress+="'"+address[i]+"',";
}
for(int j=0;j<address_small.length;j++){
newAddress_small+="'"+address_small[j]+"',";
}
newAddress=newAddress.substring(0,newAddress.length()-1);
newAddress_small=newAddress_small.substring(0,newAddress_small.length());
System.out.println("++"+newAddress);
System.out.println("--"+newAddress_small);
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<script type="javascript">
var sImgArr=new Array(<%=newAddress%>);
var sImgArrsmall=new Array(<%=newAddress_small%>);
System.out.println("++"+sImgArr);
System.out.println("--"+sImgArrsmall);
var gIndex = 0; function SlideImg(index){
gIndex=index;
if ('Microsoft Internet Explorer' == navigator.appName) {
document.getElementsByTagName("slideImg");
var imgs=document.getElementsByTagName("slideImg");
for(var i=0;i<imgs.length;i++){
 imgs[i].onclick=NextImg;
}
}
document.images["slideImg"].src = sImgArr[index];
if ('Microsoft Internet Explorer' == navigator.appName){
document.images["slideImg"].filters.item(0).play();
}
}


function SlideSmall(index){
gIndex=index;
if ('Microsoft Internet Explorer' == navigator.appName) {
document.images["slideSmall"].filters.item(1).Apply();
}
document.images["slideSmall"].src = sImgArrsmall[index];
if ('Microsoft Internet Explorer' == navigator.appName){
document.images["slideSmall"].filters.item(1).play();
}
} function NextImg(){  //显示下一张图片
gIndex = ((gIndex+1)>=sImgArr.length?0:(gIndex+1));
SlideImg(gIndex);
SlideSmall(gInddex);

}
function PrevImg(){  //显示前一张图片
gIndex = ((gIndex-1)<0?(sImgArr.length-1):(gIndex-1));
SlideImg(gIndex);
SlideSmall(gIndex);
}
</script>
</head><body>
<table width="410" height="504" border="0" align="center" cellpadding="0" cellspacing="0">
  <tr>
    <td align="center"><table width="200" height="86" border="0">
      <tr>
        <td><img name="slideImg" width="400" height="300" id="slideImg" style="BORDER-TOP: #000 1px solid; FILTER: revealtrans(duration=2.0,transition=10); BORDER-BOTTOM: #000 1px solid"></td>
      </tr>
    </table>
        <p>&nbsp;</p>
      <p>&nbsp;</p>
      <table width="200" height="55" border="0">
          <tr align="center">
            <%for(int k=0;k<address_small.length;k++){
   if(k==4){
    break;
    }
   %>
            <td height="32">&nbsp; <img name="slideSmall" id="slideSmall" style="BORDER-TOP: #000 1px solid; FILTER: revealtrans(duration=2.0,transition=10); BORDER-BOTTOM: #000 1px solid"> </td>        
            <%}%>
          </tr>
        </table>
      <table width="223" height="32" border="0">
        <tr>
          <td><a href="#" title="上一张" onclick="NextImg()">上一张</a></td>
          <td><a href="#" title="下一张" onclick="PrevImg()">下一张</a></td>
        </tr>
      </table>
      </td>
  </tr>
</table>
</body>当点击上一张，或者下一张的时候，会报这个错出来。如何解决呀
function onclick(event) {
2 PrevImg();
3 }
PrevImg is not defined