Need Some Help With Login

I am having some problems with this login script. I bought your book and love it. It has helped me out so much and it is much apreciated. This is the problem I am having. When I go to log in i get a error and I can not figure it out.

here is the script:

<?php # Login Script - V1 (login.php)
// This is the login page for the site.
require_once ('includes/config.inc.php');
if (isset($_POST['submitted'])) {
require_once (MYSQL);

// Validate the Username:
if (!empty($_POST['username'])) {
  $un = mysqli_real_escape_string ($dbc, $_POST['username']);
} else {
  $un = FALSE;
  echo '<div class="alert alert-error">You forgot to enter your username!</div>';
}

// Validate the password:
if (!empty($_POST['pass'])) {
  $p = mysqli_real_escape_string ($dbc, $_POST['pass']);
} else {
  $p = FALSE;
  echo '<div class="alert alert-error">You forgot to enter your password!</div>';
}

if ($un && $p) { // If everything's OK.
 
  // Query the database:
  $q = "SELECT user_id, user_level FROM users WHERE (username='$un' AND pass=SHA1('$p')) AND active IS NULL";
  $r = mysqli_query ($dbc, $q) or trigger_error("Query: $q\n<br />MySQL Error: " . mysqli_error($dbc));
 
  if (@mysqli_num_rows($r) == 1) { // A match was made.
  
   // Register the values & redirect:
   $_SESSION = mysqli_fetch_array ($r, MYSQLI_ASSOC);
   mysqli_free_result($r);
   mysqli_close($dbc);
  
   $url = BASE_URL . 'index.php'; // Define the URL.
   ob_end_clean(); // Delete the buffer.
   header("Location: $url");
   exit(); // Quit the script.
  
  } else { // No match was made.
   echo '<div class="alert alert-error">Either the username and password entered do not match those on file or you have not yet activated your account.</div>';
  }
 
} else { // If everything wasn't OK.
  echo '<div class="alert alert-error">Please try again.</div>';
}

mysqli_close($dbc);

} // End of SUBMIT conditional.
?>
  <div class="cnt-boxTop">SuP Clan: Account Log In</div>
  <div class="cnt-boxFiller">
   <div class="cnt-boxInfo">
   <div class="alertbox alert-frame">
    <form class="form-vertical"  action="?page=login" method="post">
	 <fieldset>
	  <div class="float-R">
	  <img alt="" height="64" src="img/lock.png" width="64" style="border:0px" />
	 </div>
	 <div class="control-group">
	   <div class="controls">
	    <div class="input-prepend">
		 <span class="add-on"><i class="icon-user"></i> </span><input placeholder="Username" type="text" class="span3" name="username" />
	    </div>
	   </div>
	 </div>
	
	 <div class="control-group">
	  <div class="controls">
	   <div class="input-prepend">
	    <span class="add-on"><i class="icon-lock"></i> </span><input placeholder="Password" type="password" class="span3" name="pass" />
	   </div>
	  </div>
	 </div>
	
	    <div class="control-group">
			 <div class="controls">
			    <input type="checkbox" id="optionsCheckbox2" value="option1" disabled> Remeber Me <span class="label label-info">Coming Soon</span>
		    </div>
		  </div>
	  
    <center><span class="label label-important">Important:</span> Your browser must allow cookies in order to log in.</center>
	
	 </fieldset>
	 <hr>
	
	 <div align="center"><button type="submit" class="btn btn-primary" /><span class="add-on"><i class="icon-ok"></i> </span>Log In</button> <a class="btn btn-warning" href="#"><span class="add-on"><i class="icon-refresh"></i> </span>Forgot Password?</a></div>
	  <input type="hidden" name="submitted" value="TRUE" />
    </form>
    </div>
   </div>
  </div>
  <div class="cnt-boxFoot">
   <div class="author"></div>
  </div>
</div>

PHP for the Web: Visual QuickStart Guide → PHP for the Web: Visual QuickStart Guide (4th Edition) → Ch 13 Pursue - Make Login Form Sticky Started by Scatz29 , 6 May 2013 login, sticky, pursue, chapter 13	2 replies 62 views	Scatz29 7 May 2013
PHP Advanced: Visual QuickPro Guide → PHP 5 Advanced: Visual QuickPro Guide (2nd Edition) → Having Trouble Establishing Sessions After Login In Modular Configuration Started by danconia , 19 Apr 2013 sessions, modular, login, php	1 reply 82 views	HartleySan 19 Apr 2013
Single Editions → Effortless E-Commerce with PHP and MySQL → Problem With Login Started by MrJames , 22 Dec 2012 login, register, php, mysql	8 replies 466 views	Larry 30 Dec 2012
Single Editions → Effortless E-Commerce with PHP and MySQL → Improvement On Login System Started by honjian5231 , 20 Nov 2012 login, e-comerce, php, mysql and 3 more...	3 replies 379 views	Marie 4 Jan 2013
Single Editions → The Yii Book → Unknown_Identity Error Started by mint , 23 Jun 2012 database, login	2 replies 356 views	mint 24 Jun 2012

Translating Geek Into English

#1 Logic

#2 HartleySan

#3 Logic

#4 Larry

Also tagged with one or more of these keywords: login

Ch 13 Pursue - Make Login Form Sticky

Having Trouble Establishing Sessions After Login In Modular Configuration

Problem With Login

Improvement On Login System

Unknown_Identity Error