jQuery hide（）执行错误

I have built an AJAX driven form wherein when i press the submit button,it displays data via AJAX.All that is working fine.Now i want to hide a specific too as a part of the AJAX function.But instead of just hiding that the whole page goes blank!Heres the code The AJAX function:

function ajax_post(){
$("#form1").hide();
var hr = new XMLHttpRequest();


var url = "my_parse_filefe.php";
var fn = document.getElementById("description").value;
  var nm = document.getElementById("name").value;
  var sel = $('#list option:selected').text()

 var vars = "todo="+fn+"&name="+nm+"&sel="+sel;
hr.open("POST", url, true);

hr.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
hr.onreadystatechange = function() {
    if(hr.readyState == 4 && hr.status == 200) {
        var return_data = hr.responseText;
        document.getElementById("status").innerHTML = return_data;
    }
}
hr.send(vars);

}

The PHP in the same file:

<?php
include_once "connect_to_mysql.php";
$sql = mysql_query("SELECT * FROM timetracking");
while($row = mysql_fetch_array($sql))
 {$name = $row['name'];
 $description = $row['description'];
 $hours = $row['hours_invested'];
 $finaltable1 .= '<table class="ftable" width="650">
<tr>
<td align="center">'.$name.'</td>
<td align="center">'.$description.'</td>
<td align="center"> '.$hours.'</td>
</tr>
';}
?>
<div id="form1"><?php print $finaltable1; ?> </div>
<div id="status"></div>

Note:When I put normal text inside the "form1" div it works!when i put php tags it stops working.