I am sending multiple AJAX request through a loop, but some request are successfully send not all.. my code goes here...

for(var i=0; i<dataArray.length; i++)
{
      var request=getHttpRequest();
      request.open('post','update.php',false);
      request.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
      request.send("data="+dataArray[i]);

      if(request.readyState == 4)
      {
            alert("updated the data="+dataArray[i]);
      }
}

           function getHttpRequest()
           {
               var request=false;
               if(window.XMLHttpRequest)
               {
                   request=new XMLHttpRequest();
               }
               else if(window.ActiveXObject)
               {
                   try
                   {
                       request=new ActiveXObject("Msxml2.XMLHTTP");
                   }
                   catch(e)
                   {
                       try
                       {
                           request=new ActiveXObject("Microsoft.XMLHTTP");
                       }
                       catch(e)
                       {
                           request=false;
                       }
                   }
               }

               return request;
           }

here in the above code, some data are being posted, but some dont, it does not return the readyState = 4. i.e if i have array with dataArray['1','2','3','4']; it updates only 1,2,and 4 and skips 3, or other value in between... is there any solution..please help...