按钮返回不能在IE7上工作

我有一个按钮预览的这个函数，这个代码在所有版本的IE中工作，在IE7中更少。IE7的按钮不工作。为什么?我该如何解决这个问题?

<?php    
//////// --- BUTTON BACK  : CHARGE THE QUERY OF BEFORE PAGE WHEN WE PRESS BACK ---/////////////    
 if ( isset($_POST['back'])){     
    $_SESSION['onpage']=$_SESSION['onpage']-1;
    $query_questionset= "select Q.Constructor AS Constructor,
                            QS.QuestionIDFKPK AS QuestionIDFKPK,
                            Q.QuestionValue AS QuestionValue,
                            QS.SortOrder AS SortOrder,
                            QS.onpage AS onpage
                         from tbluserset AS US
                         inner join tblquestionset AS QS ON 
                                 US.QuestionSetIDFKPK = QS.QuestionSetIDPK
                        inner join tblquestion AS Q ON 
                                 QS.QuestionIDFKPK = Q.QuestionIDPK
                        where (US.UserIDFKPK = ".$UserId.")
                         and (US.UserSetIDPK= '".$_SESSION['UserSetIDPK']."')
                         and (QS.onpage = '".$_SESSION['onpage']."')
                        order by QS.SortOrder";
    if($_SESSION['onpage']==0){         
        $_SESSION['controluserupdate']=1;
    }//<-END CASE ONPAGE=0
}//<- END POST [BACK]   
?>       
<script>    
function postBack() {    
                    var myForm = document.getElementById("formID");
                    var backInput = document.createElement("input");
                    backInput.type = "hidden";
                    backInput.name = "back";
                    backInput.value = "1";
                    myForm.appendChild(backInput);
};
</script>
< html>
 ..
 ....
< form id= "formID"  name="formID" class="formular"   method="post" action= "<?= $url = "QUESTIONAREFINISHING.php"; ?>" accept-charset="utf-8">

<div id="footer"> <!-- DIV FOOTER CONTAINER BUTTONS OUTSIDE BOX QUESTIONAIRE--> 
    <?php   if($_SESSION['onpage'] >=1 && $_SESSION['onpage'] <= $_SESSION['MaxOnPage']-1){ ?>          
        <div><button class="botonesform"  type="hidden"  onclick="postBack()" name="back"  value="" > &#8592 Back  </button ></div>             
        <input class="botonesform" type="submit" name="submit" onclick="probandosubmit()" value="Forward &#8594" />          
    <?php   } ?>
</div>
</form>
..
..
</html>