Problem ajax login form (explorer)

1

i cant send more then once query on explorer to ajax but can send on firefox. how can i fix this.


<script type="text/javascript">
if(window.ActiveXObject){
    xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
}else if(window.XMLHttpRequest){
    xmlHttp = new XMLHttpRequest();
}

function cm(v1,v2){
    xmlHttp.onreadystatechange=cm_ok;
    q="cm.php?username="+v1+"&password="+v2;
    xmlHttp.open("GET",q,true);
    xmlHttp.send(null);
}

function cm_ok(){
    if (xmlHttp.readyState==4 || xmlHttp.readyState=="complete"){
        if(xmlHttp.responseText=="0") {
            error("username","Invalid username or password");
            error("password","");
        }else{
            success("username","u r in...");
            success("password","");
        }
    }
}

function success(v1,v2) {document.getElementById(v1+'_msg').innerHTML=v2; document.getElementById(v1+'_msg').className="success"; document.getElementById(v1).className="success_border";}
function error(v1,v2) {document.getElementById(v1+'_msg').innerHTML=v2; document.getElementById(v1+'_msg').className="error"; document.getElementById(v1).className="error_border";document.getElementById(v1).focus();}

function validate(){
    var username = document.getElementById('username').value;
    var password = document.getElementById('password').value;
    
    if(username=="") error("username","Username?"); else success("username","");
    if(password=="") error("password","Password?"); else success("password","");
    if(username != "" && password != "") cm(username,password);
}

function ep(e){
    if(e.keyCode==13) validate();
}
</script>

<form autocomplete="off">
<table width="500" border="0" align="center" cellpadding="4" cellspacing="1" bgcolor="#677247">
    <tr>
      <td width="100" bgcolor="#F5F7F0">username</td>
      <td bgcolor="#F5F7F0"><input name="username" type="text" id="username" onKeyPress="ep(event);"> <span id="username_msg"></span></td>
    </tr>
    <tr>
      <td bgcolor="#F5F7F0">password</td>
      <td bgcolor="#F5F7F0"><input name="password" type="text" id="password" onKeyPress="ep(event);"/> <span id="password_msg"></span></td>
    </tr>
    <tr>
      <td bgcolor="#F5F7F0">&nbsp;</td>
      <td bgcolor="#F5F7F0"><input type="button" name="Submit" value="Submit" onClick="validate();"/></td>
    </tr>
  </table>
</form>

cm.php


<?
include "db.php";
$username=$_GET["username"];
$password=$_GET["password"];
$q="select * from users where username='$username' and password='$password' ";
$res= mysql_query($q) or die("Query failed : " . mysql_error());
$nr=mysql_num_rows($res);
if($nr==0) echo "0"; else echo "1";
?>