Warning: mysql_fetch_array(): error. Help Please

Hello everyone, I'm currently building a cms system and have hit a brick wall in relation to the error I'm getting below. Any help would be greatly appreciated.

Thanks James.

The error:
Warning: mysql_fetch_array(): supplied argument is not a valid MySQL result resource in C:\wamp\www\widget_corp\includes\functions.php on line 41

The functions.php:

<?php
// This is the place to store basic functions.

    function confirm_query($result_set) {
        if (!Sresult_set) {
            die ("database query failed: " . mysql_error());
        }
    }

    function get_all_subjects() {
        global $connection; 
        $query = "SELECT*
                FROM subjects 
                ORDER BY position ASC";
        $subject_set = mysql_query($query, $connection);
        confirm_query($subject_set);
        return $subject_set;
    }

    function get_pages_for_subject($subject_id){
        global $connection; 
        $query ="SELECT*
                FROM pages 
                WHERE subject_id ={$subject_id}
                ORDER BY position ASC";
        $page_set = mysql_query($query, $connection);
        confirm_query($page_set);   
        return $page_set;
    }

    function get_subject_by_id($subject_id) {
        global $connection;
        $query = "SELECT * ";
        $query .= "FROM subjects ";
        $query .= "WHERE id=" . $subject_id ." ";
        $query .="LIMIT 1";
        $result_set = mysql_query($query, $connection);
        confirm_query($result_set);
        //: REMEMBER
        // If no rows are returned, fetched array will return false
**** ERROR LINE REFERED ABOVE****if ($subject = mysql_fetch_array($result_set)) {
            return $subject;
        } else {
            return NULL;
        }
    }
    function get_page_by_id($page_id) {
        global $connection;
        $query = "SELECT * ";
        $query .= "FROM pages ";
        $query .= "WHERE id=" . $page_id ." ";
        $query .="LIMIT 1";
        $result_set = mysql_query($query,$connection);
        confirm_query($result_set);
        //: REMEMBER
        // If no rows are returned, fetched array will return false
        if ($spage = mysql_fetch_array($result_set))  {
            return $page;
        } else {
            return NULL;
        }
    }
?>

Not sure if its needed but here is the main content php file whichs calls the functions file.

content.php
<?php require_once("includes/connection.php"); ?>
<?php require_once("includes/functions.php"); ?>
<?php
    if (isset($_GET['subj'])){
        $sel_subject = get_subject_by_id($GET['subj']);
        $sel_page = NULL;
    } elseif (isset($_GET['page'])){
    $sel_subject = NULL;
    $sel_page = get_page_by_id($_GET['page']);
    } else {
        $sel_subject = NULL;
        $sel_page = NULL;
    }
?>
<?php include("includes/header.php"); ?>
<table id="structure">
                <tr>
                    <td id="navigation"> 
                        <ul class="subjects">
                    <?php
                    $subject_set = get_all_subjects();
                    while ($subject = mysql_fetch_array($subject_set)) {
                        echo "<li";
                        if ($subject["id"] == $sel_subject['id']) {
                            echo " class=\"selected\"";
                        }
                        echo "><a href=\"content.php?subj=" .urlencode($subject["id"])
                        ."\">{$subject["menu_name"]}</a></li>";

                        $page_set = get_pages_for_subject($subject["id"]);
                    echo"<ul class=\"pages\">";
                    while ($page = mysql_fetch_array($page_set)) {
                        echo "<li";
                        if ($page["id"] == $sel_page['id'])  {
                            echo " class=\"selected\"";
                        }
                        echo "><a href =\"content.php?page=" . urlencode($page["id"]) ."\"> {$page["menu_name"]}</a></li>";
                    }
                    echo "</ul>";

                    }
                    ?>
                        </ul>
                    </td>
                    <td id="page">
                    <?php if (!is_null($sel_subject)) {//subject selected ?>
                        <h2> <?php echo $sel_subject['menu_name']; ?></h2>
                    <?php } elseif (!is_null($sel_page)) {//page selected ?>
                        <h2> <?php echo $sel_page['menu_name']; ?></h2>
                        <div class="page-content">
                            <?php echo $sel_page['content']; ?>
                         </div>
                    <?php } else { // nothing selected ?>
                        <h2> Select a subject or page to edit </h2>
                    <?php } ?>
                       <br />                
                    </td>
                </tr>
             </table>
<?php require("includes/footer.php"); ?>