Cannot modify header information

Hej jeg vil gerne have nedestående kode til at gå til
header("Location: index.php?sejlerprofil");
når den har køre mysql_query . men fejler hvad gør jeg

<?php
include(realpath("./include") . "./inc/db.inc");
$res = mysql_query("SELECT * FROM booking where id = '$event'  " );

$number = @mysql_num_rows($res);
$row = @mysql_fetch_assoc($res);


$today = date("Ymd");                          // Giver dagsdato og tid

$event_id = ($row["id"]);
$event_user = ($row["event_user"]);
$book_date = ($row["book_date"]);
$date_start = ($row["date_start"]);
$date_end = ($row["date_end"]);
$time_start = ($row["time_start"]);
$time_end = ($row["time_end"]);
$event_type = ($row["event_type"]);
$boatid = ($row["boatid"]);
$seclevel = ($row["seclevel"]);
$note = ($row["note"]);




if (isset($_POST['edit'])) {
$event_id = ($_POST["event_id"]);
$event_user = ($_POST['event_user']);
$book_date = ($_POST['book_date']);
$date_start = ($_POST['date_start']);
$date_end = ($_POST['date_end']);
$time_start = ($_POST['time_start']);
$time_end = ($_POST['time_end']);
$event_type = ($_POST['event_type']);
$boatid = ($_POST['boatid']);
$seclevel = ($_POST['seclevel']);
$note = ($_POST['note']);



$send_event = "Update booking set event_user='$authenticatedUser',  book_date='$today', date_start='$date_start', date_end='$date_end' ,  time_start='$time_start' , time_end='$time_end', event_type='$event_type', boatid='$boatid', seclevel='$seclevel', note='$note' where id ='$event_id' " ;

echo $send_event;
##echo "Posten er rettet";
mysql_query($send_event) or die (mysql_error());



header("Location: index.php?sejlerprofil");


}

;


?>

<form action="index.php?pageid=edit_event" method="post">
<h1>Vis/add event</h1>
<hr style="margin-left:5px;" />
<table border="0" cellspacing="2" colspacing="2" style="margin:5px;">
  <tr>
    <td>Brugernavn</td>
    <td><?=$authenticatedUser?></td>
  </tr>
  <tr>
    <td><font color="">Vælg booking type:</font></td>
    <td>
      <select size="1" name="event_type" value="<?=$event_type?>"
      <option selected="selected" value="Weekendtur">Weekendtur</option>
        <option value="Ugentlig sejlads">ugentlige sejladser</option>
        <option value="Klargøringsweekend">klargøringsweekend</option>
        <option value="Afrigningsweekend">Afrigningsweekend</option>
        <option value="Instruktørmde">Instruktørmøde</option>
        <option value="Privat">Privat</option>
        <option value="Andet">Andet</option>
        <option value="Sommerferie">Sommerferie</option>
        <option value="Weekendtur">Weekendtur</option>
      </select>
    </td>
  </tr>
  <tr>
    <td>Start dato(YYYY-MM-DD)</td>
    <td><input type="text" name="date_start" value="<?=$date_start?>" size=10></td>
    <td>Start tidspunkt (hr:mn)</td>
    <td><input type="text" name="time_start" value="<?=substr("$time_start", 0, 5);?>" size=5></td>
  </tr>
  <tr>
    <td>Slut dato (YYYY-MM-DD) </td>
    <td><input type="text" name="date_end" value="<?=$date_end?>" size=10></td>
    <td>Slut tidspunkt (hr:mn)</td>
    <td><input type="text" name="time_end" value="<?=substr("$time_end", 0, 5);?>" size=5></td>

  </tr>
  <tr>
    <td>Vælg bådnummer:</font></td>
    <td>
  <select size="1" name="boatid" value="<?=boatid?>">
        <option selected="selected" value="1">Båd 1</option>
        <option value="2">Båd 2</option>
        <option value="3">Båd 3</option>
        <option value="4">Båd 4</option>
      </select>
    </td>
  </tr>
  <tr>
    <td>Synlig for :</font></td>
    <td>
      <select size="1" name="seclevel" value="<?=$seclevel?>">
      <option selected="selected" value="1">Kun mig selv</option>
    <option value="2">Alle Instruktører</option>
    <option value="3">Alle</option>
      </select>
</td>
  </tr>
<tr>
  <td>Noter:</td>
  <td><textarea name="note"  value="<?=$note?>" rows="5" cols="20"><?=$note?></textarea></td>
</tr>
  <tr>
<tr>
    <td><input type="submit" name="edit" value="ret event"></td>
    <input type="hidden" name="event_id" value="<?=$event_id?>">
  </tr>
</table>
</form>