服务器返回的数据与XMLHttpRequest接收到的数据怎么不一样啊?

客户端脚本<script language="javascript" type="text/javascript">
        function GetAjaxValue(url)
        {
            var randomNum = Math.random();
            var objXMLHttp;
            if(window.ActiveXObject)
            {
                xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
            }
            else if(window.XMLHttpRequest)
            {
                xmlHttp = new XMLHttpRequest();
            }    
            xmlHttp.Open("GET",url,false);
        xmlHttp.Send(null);
        var returnValue;
        if(xmlHttp.readyState == 4)
        {
            if(xmlHttp.status == 200)
            {
                returnValue = xmlHttp.responseText;
            }
            else
            {
                returnValue = xmlHttp.responseText;
            }
        }
        else
        {
            returnValue = xmlHttp.responseText;
        }
        
        return(returnValue);  
        }
        
        var url = "../SetSession.aspx";
        window.open('../SetSession.aspx','test','width:1200px;height:700px');
        var temp = GetAjaxValue(url);    </script>
服务端代码protected void Page_Load(object sender, EventArgs e)
    {
        try {
            // 执行相关操作            Response.Write(("true"));
        }
        catch (Exception ex) {
            Response.Write(ex.Message);
        }
        finally {
            Response.End();
        }
    }
window.open('../SetSession.aspx','test','width:1200px;height:700px')
返回的是true
可是temp 是页面出错信息的一大堆代码,而且中文都是乱码不知道是什么错误
请帮忙看一下
谢谢