SQL error when using ft_api_check_submission_is_unique

Code:
<?php

require_once("../[directory]/global/api/api.php");

$fields = ft_api_init_form_page(28);



$already_exists = "";



// validation time!

$errors = array();

if (isset($_POST['submit']))

{

  $rules = array();

  $rules[] = "required,how_they_heard_about_us,Please select a referral source.";

  $rules[] = "required,email,Please enter your email address.";

  $errors = validate_fields($_POST, $rules);

 

  // no errors - great! Now we process the page. The ft_api_process_form does

  // the job of both updating the database and redirecting to the next page

  if (empty($errors))

  {

    $params = array(

      "submit_button" => "submit",

      "next_page" => "thanks.php",

      "form_data" => $_POST,

      "finalize" => true

    );

    

    

$criteria = array(

  "email" => $_POST["email"]

);

if (ft_api_check_submission_is_unique(28, $criteria))

{

  // uh-oh! A submission already exists with this email address! Abort, abort! 

  // here, you could do something like set a variable like: $already_exists = true

  // and in the webpage do a little test to see if it's set. If so, let the user know 

  // what's going on

  

  $already_exists = true;

  

}

else

{

  // call ft_api_process_form function here to continue processing the form submission

    ft_api_process_form($params);

  

  

}











  }

}

?>



<html>





<head>

</head>

<body>



<? if($already_exists == true) { echo("**This email already exists**<br/><br/>"); } ?>



<?php

// if $errors is not empty, the form must have failed one or more validation 

// tests. Loop through each and display them on the page for the user

if (!empty($errors))

{

  echo "<div class='error'>Please fix the following errors:\n<ul>";

  foreach ($errors as $error)

    echo "<li>$error</li>\n";

 

  echo "</ul></div>"; 

}

?>





Join our mailing list for league and tournament updates:

<form action="<?php echo $_SERVER["PHP_SELF"]?>" method="POST">



    <input type="text" name="email" size="30" value="<?=htmlspecialchars(@$fields["email"])?>">

    <select name="how_they_heard_about_us">

        <option value="">Your Referral Source</option>

        <option value="MySpace">MySpace</option>

        <option value="Facebook">Facebook</option>

        <option value="Search Engine">Search Engine</option>

        <option value="Friend">Friend</option>

        <option value="Advertisement">Advertisement</option>

        <option value="Other">Other</option>

    </select>&nbsp;

    <input type="submit" name="submit" value="submit">



</form>



</body>

</html>