多个XMLHttpRequest

I call ajax request in a loop. Around 20 of them. But few are getting aborted. How can I avoid that ?

Most of them are getting aborted.

function callURLAsync(url) 
{
  var xmlHttpReq = false;
    var self = this;
    // Mozilla/Safari
    if (window.XMLHttpRequest) 
    {
        self.xmlHttpReq = new XMLHttpRequest();
    }
    // IE
    else if (window.ActiveXObject) 
    {
        self.xmlHttpReq = new ActiveXObject("Microsoft.XMLHTTP");
    }

    self.xmlHttpReq.open('POST', url, true);
    self.xmlHttpReq.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');

    self.xmlHttpReq.onreadystatechange = function() 
    {
        if (self.xmlHttpReq.readyState == 4) {
        }
    }

    self.xmlHttpReq.send();
}

function startLogout(){

    for(var i=0;i< 20;i++){
        callURLAsync("myDummyURl");
    }

}

Thanks Sailesh