title: Many js XMLHttpRequest running at the same time causing one of them to return an empty string?
body: <p>I prefer to not use jQuery (as much as I understood the file is relately big and everytime the page loads it will "eat" a lot of bandwidth). I checked my code (below) that XMLHttpRequest is writted properly, and is NOT cross-domain. On Chrome is working properly, but on IE, if only one request is running then no problem, but the code below using 2 instances of XMLHttpRequest and BOTH somehow accessing my CGI but returns always empty string. 
  I have tried also send(null), send("") or send(''). </p>
  
  <p>My code: </p>
  
  <pre><code>&lt;script type="text/javascript"&gt;
  var SMR;
  var UPR; 
  var F;
  var G;
  function MUPD() { 
      F = window.setInterval(Updator, 5000); 
      G = window.setInterval(Listener, 5000); 
      if(typeof XMLHttpRequest !== 'undefined') { SMR = new XMLHttpRequest(); UPR = new XMLHttpRequest(); }
      else {  
          var versions = ["MSXML2.XmlHttp.5.0",   
                          "MSXML2.XmlHttp.4.0",  
                          "MSXML2.XmlHttp.3.0",   
                          "MSXML2.XmlHttp.2.0",  
                          "Microsoft.XmlHttp"]  
          for(var i = 0, len = versions.length; i &lt; len; i++) {  
              try {  
                  SMR = new ActiveXObject(versions[i]);  
                  UPR = new ActiveXObject(versions[i]);  
                  break;  
              }  
              catch(e){}  
           }  
      } 
  }
  function Updator() { 
      if (document.cookie.length &gt; 0) { 
       var begin = document.cookie.indexOf("TCPID="); 
           if (begin != -1) {             
              var end = document.cookie.indexOf(";", begin+6);
      if (end == -1) end = document.cookie.length;
      var fupd=UPD(unescape(document.cookie.substring(begin+6, end))).split("-");
      if(fupd[0]=="OK") { 
          for(var i=1 ; i&lt;fupd.length ; i+=2) {
              var elm=document.getElementByID("I"+fupd[i]);
              elm.setAttribute("src", "/theclub/cgi-bin/personalimage.cgi?UID="+fupd[i]);
              if(fupd[i+1].toString()!=="OFF") { document.getElementById("T"+fupd[i]).innerHTML=fupd[i+1]; }
          }
      }
       }
       else { window.top.location.href="/theclub/login.htm?MOD=NEW"; }
      }
  }
  function UPD(cvl) { 
  try {
      UPR.open("GET", "/theclub/cgi-bin/chkpubupd.cgi?CVL="+cvl, false);
      UPR.setRequestHeader("Content-type", "text/x-www-form-urlencoded");
          UPR.send('');
          if (UPR.status == 200) { return UPR.responseText; }
          else { alert("Error: "+UPR.status+" &gt;&gt; "+UPR.responseText); return ""; }
  }
  catch (e) { alert("Error in updating system"); return ""; } 
  }
  function PWR(cvl) {
  try {
      SMR.open("GET", "/theclub/cgi-bin/getmessages.cgi?CVL="+cvl, false); 
          SMR.send('');
          if (SMR.status == 200 &amp;&amp; SMR.responseText!=="") { alert(SMR.responseText);}
          else if(SMR.status != 200) { alert(SMR.status+" &gt;&gt; "+SMR.responseText); }
      }
  catch (e) { alert("Error receiving messages"); } 
  }
  function Listener() {
      if (document.cookie.length &gt; 0) { 
       var begin = document.cookie.indexOf("TCPID="); 
           if (begin != -1) {
              var end = document.cookie.indexOf(";", begin+6);
      if (end == -1) end = document.cookie.length;
      PWR(unescape(document.cookie.substring(begin+6, end)));
       }
       else { window.top.location.href="/theclub/login.htm?MOD=NEW"; }
      }
  }
  ...
  &lt;/script&gt;
  </code></pre>