problem during data update in php ajax

ajax code-

xmlhttp.open("GET","voting.php?qid="+qid+"&uid="+uid+"&type="+type,true);

html-

<td ><img src="images/up.jpeg" style="border:none;" title="Like" 
                onclick="doVote('<?php echo $q_id; ?>','<?php echo $_SESSION['UserId']; ?>','up')"></td>

problem: qid is getting passed to voting.php page but uid and type are not.Why?

try

xmlhttp.open("GET","voting.php?qid="+qid+"&uid="+uid+"&type="+type,true);

?