ajax类使用过程出现的问题请教.

在执行到xmlhttp.Send()时出现对象不支持此属性和方法的错误,请大家帮看一下什么原因.我把xmlhttp.send()注掉时就没有错误提示,但肯定就没有办法完成功能了.
源码如下:

 1function ajaxSubmit(){
 2 //获取用户表单的内容
 3 var WillBuyId = form1.WillBuyId.value;
 4 var FullName=form1.FullName.value;
 5 var Tell=form1.Tell.value;
 6 var Address=form1.Address.value;
 7 var PostCode=form1.PostCode.value;
 8 var Content=form1.Content.value;
 9 var url;
10 url ="WillBuyId="+escape(WillBuyId)+"&FullName="+escape(FullName)+"&Tell="+escape(Tell)+"&PostCode="+escape(PostCode)+"&Address="+escape(Address)+"&Content="+escape(Content);
11 //创建XMLHttpRequest对象
12 var xmlhttp=new XMLHttpRequest(); 
13 xmlhttp.method="Post";
14 xmlhttp.url="bin/savewillBuyRe.asp";
15    xmlhttp.content=url;
16
17 // 设置回调函数，输出响应内容
18 xmlhttp.callback=function(xmlobj) {
19  form1.Content.value="";
20     msg.innerHTML = "数据提交成功"; 
21 }
22 xmlhttp.send();    /*发送请求*/
23}
24</script>
25

引用的ajax.js代码如下

 1// AJAX类
 2function XMLHttpRequest() {
 3    var xmlObj = false;
 4    var CBfunc,ObjSelf;
 5    ObjSelf=this;
 6    try { xmlObj=new XMLHttpRequest; }
 7    catch(e) {
 8        try { xmlObj=new ActiveXObject("MSXML2.XMLHTTP"); }
 9        catch(e2) {
10            try { xmlObj=new ActiveXObject("Microsoft.XMLHTTP"); }
11            catch(e3) { xmlObj=false; }
12        }
13    }
14    if (!xmlObj) return false;
15    this.method="POST";
16    this.url;
17    this.async=true;
18    this.content="";
19    this.callback=function(cbobj) {return;}
20    this.send=function() {
21        if(!this.method||!this.url||!this.async) return false;
22        xmlObj.open (this.method, this.url, this.async);
23        if(this.method=="POST")
24            xmlObj.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
25        xmlObj.onreadystatechange=function() {
26            if(xmlObj.readyState==4) {
27                if(xmlObj.status==200) {
28                    ObjSelf.callback(xmlObj);
29                }
30            }
31        }
32        if(this.method=="POST") xmlObj.send(this.content);
33        else xmlObj.send(null);
34    }
35}