＆＃39;空＆＃39;在IE8上的javascript错误上为null或不是对象

Question

下一个代码向我显示如下错误：＆＃34; null＆＃39;是null或不是对象＆＃34;仅在IE8上。 IE8显示＆＃34;} catch（错误）{＆＃34;怎么回事。我一直在研究这个问题。在一篇文章中我发现你可以解决这个问题：window.event。但我不知道在哪里使用它。请帮忙。

<![CDATA[
     var sendRequest = function(url, callback, postData) {

        try{
        var req = createXMLHTTPObject();
        if (!req) return;
        var method = (postData) ? "POST" : "GET";
        req.open(method, url, true);
        req.setRequestHeader('User-Agent','XMLHTTP/1.0');
        if (postData)
          req.setRequestHeader('Content-type','application/x-www-form-urlencoded; charset=UTF-8');
          req.timeout = 65000;
          req.ontimeout = function () { ajaxRequestTimedOut(); }
          req.onreadystatechange = function () {
            try{
              if (req.readyState != 4) return;
              if (req.status != 200 && req.status != 304) {
                unlockScreen();
                openAlert('<p class="style6" style="text-align: justify;"> Error de comunicación. Presiona Aceptar para continuar.');
                lockScreen();
                setTimeout(function(){
                  sendRequest(url, callback, postData);
                  }, 500);
                return;
              }
              callback(req);
            }catch(err){ //IE8 Says this line is wrong
              openAlert('<p class="style6" style="text-align: justify;">' + err.message);         
            } 
          }
        if (req.readyState == 4) return;

        //Fix to prevent Aborted messages on IE
        req.onprogress = function () { };
        req.onerror = function () { };
        req.onabort = function(){
          unlockScreen();
          openAlert('<p class="style6" style="text-align: justify;">' + "Ocurrio un problema, favor de reintentar.");
          };
        setTimeout(function(){
          req.send("SoapRequest=" + escape(postData));
          }, 500);

      }catch(err){
        openAlert('<p class="style6" style="text-align: justify;">' + err.message);
      }
    };
    ]]>

出了什么问题？非常感谢你！