session jeg fatter det ikke

ja jeg prøver at lave en session, men den kommer med følgene fejlmelding:

Warning: session_start(): Cannot send session cache limiter - headers already sent (output started at /web/www/frac/users/punkt/edit.php:1) in /web/www/frac/users/punkt/edit.php on line 2

min kode:

  <?php
  session_start();                              ///// <--
  include("include/head.php");
  $nr = $_GET["nr"];
  $conn = mysql_connect("localhost", "punkt", "********") or die(mysql_error());
  mysql_select_db("punkt") or die(mysql_error());

  $result = mysql_query("select * from members
where nr='$nr'");
  while($row = mysql_fetch_array($result))
  {
    $nick = stripslashes($row["nick"]);
    $info = stripslashes($row["info"]);
    $age = stripslashes($row["age"]);
    $favmap = stripslashes($row["favmap"]);
    $favwep = stripslashes($row["favwepon"]);
    $pass = stripslashes($row["pass"]);
    session_register(pass);                          /// <--