[RESOLVED] Not sure why I get this warning

[asa_carter]

What would cause me to get this warning?

Warning: Unknown(): Your script possibly relies on a session side-effect which existed until PHP 4.2.3. Please be advised that the session extension does not consider global variables as a source of data, unless register_globals is enabled. You can disable this functionality and this warning by setting session.bug_compat_42 or session.bug_compat_warn to off, respectively. in Unknown on line 0

[ClarkF1]

If you posted some code we could tell you.

[asa_carter]

<? session_start();
setcookie(curl, $_SERVER['REQUEST_URI'], time()+3600, '/');
$valid_user = $_SESSION['valid_user'];
$user = $_SESSION['user'];
$u = $_GET['u'];
$v = $_GET['v'];

if (session_is_registered("valid_user")) { header("location: index.php"); exit; }

include("connect.php");
$result = mysql_query("UPDATE login SET verify = 'verified' WHERE userid = '$u' AND verify = '$v'");
if (($user) || (mysql_affected_rows==1))
{
  $update=true;
  if ($user)
  {
    $valid_user = $user;
    session_unregister("user");
  }
  else
    $valid_user = $u;
  session_register("valid_user");
}
include("header.php");
$nav_title="Open Account";
include("navbar.php");
include("tab3.php");
?>
<div class="content">
  <?
  if ($update==true)
  {
    ?>
	<h1>Congratulations</h1>
    <p>Your email address was verified sucessfully. You can now bid, buy and sell.</p>
	<p>What would you like to do now?</p>
    <ul>
    <li><a class="co" href="buy.php"><b>Browse our categories</b></a></li>
    <li><a class="co" href="sell.php"><b>Sell something</b></a></li>
    <li><a class="co" href="my_auction.php"><b>View your account details</b></a></li>
    </ul>
	<?
  }
  else
  {
    ?>
    <h1>There is a problem</h1>
	<?
	$result = mysql_query("SELECT * FROM login WHERE userid='$u' AND verify='verified'");
    if (mysql_num_rows($result)>0)
	{
      echo "<p>The email address for <b>$u</b> has already been verified.</p>";
	  echo "<ul><li><a class=\"co\" href=\"sign_in.php\"><b>Sign in to access your account</b></a></li></ul>";
	}
	else
	{
      ?>
	  <p>We could not verify your email address.</p>
   	  <p>The reason for this might be:</p>
      <ol>
      <li>The email address has already been verified.</li>
      <li>The verification number is incorrect.</li>
      </ol>
   	  <p>If you cannot click the link in the email we sent, please ensure it is copied and pasted correctly in your web browser.</p>
      <?
	}
  }
  ?>
  <table height="1" cellpadding="0" cellspacing="0" width="100%"><tr></tr></table>
</div>
<? include("footer.php"); ?>

[Weedpacket]

Don't go around mixing $_SESSION and session_unregister()/session_register()/session_is_registered(). The manual explicitly warns against this on the pages for all three functions (which also provides more appropriate methods).