验证所输入的数据。。跟数据库是否重复

高手看下。运行后老是出错。要怎么改帮忙看看谢谢

主页面：数据库表landed。字段name
<script language="javascript" type="text/javascript">
var xmlHttp = false;
try {
xmlHttp = new ActiveXObject("Msxml2.XMLHTTP");
} catch (e) {
try {
xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
} catch (e2) {
xmlHttp = false;
}
}
if (!xmlHttp && typeof XMLHttpRequest != 'undefined') {
xmlHttp = new XMLHttpRequest();
}

function callServer() {
var u_name = document.getElementById("u_name").value;
if ((u_name == null) || (u_name == "")) return;
var url = "cu.asp?name=" + escape(u_name);
xmlHttp.open("GET", url, true);
xmlHttp.onreadystatechange = updatePage;
xmlHttp.send(null);
}

function updatePage() {
if (xmlHttp.readyState < 4) {
test1.innerHTML="loading...";
}
if (xmlHttp.readyState == 4) {
var response = xmlHttp.responseText;
test1.innerHTML=response;
}
if (test1.innerHTML=="已被注册"){
document.form1.submit.disabled=true}else{
document.form1.submit.disabled=false
}
}
</script>

<form name="form1" action="t1.asp" method="post" autocomplete="off">
用户名: <input type="text" name="u_name" id="u_name" onChange="callServer();" />
<span id="test1">是否能注册</span><br>
密码：<input type="password" />
<input type="submit" name="submit" value="注册" />
</form>

cu.asp

<%
Response.Buffer = True
Response.ExpiresAbsolute = Now() - 1
Response.Expires = 0
Response.CacheControl = "no-cache"
Response.AddHeader "Pragma", "No-Cache"
%>
<%
name=request.querystring("u_name")
Set rs = Server.CreateObject ("ADODB.Recordset")
sql = "Select * from landed where name='"&name&"'"
rs.Open sql,conn,1,1
if rs.eof and rs.bof then
response.write("可以注册")
else
response.write("已被注册")
end if
rs.close
set rs=nothing
call CloseDatabase
%> --------------------编程问答-------------------- 有什么问题，你把sql 显示出来看看，放到数据库查询中试试 --------------------编程问答-------------------- function callServer() {
var u_name = document.getElementById("u_name").value;
if ((u_name == null) || (u_name == "")) return;
var url = "cu.asp?name=" + escape(u_name);
xmlHttp.open("GET", url, true);//这边有可能错
alert('执行到了！');
xmlHttp.onreadystatechange = updatePage;
alert('updatePage执行到了！');
xmlHttp.send(null);
alert('updatePage已经结束！');
}
--------------------编程问答-------------------- ajax
也要直接在外部看看Connections/xt.asp返回的是什么。

补充：.NET技术 ,  VB.NET