codeigniter - jQuery Tablesorter not work with CodeIgniter

Question

I downloaded Tablesorter and it works fine but if I use in codeigniter firebug says c is undefined on select different value from dropdown.

I move all js resource files inclusion in views/template/header/

header.php

<!-- Tablesorter -->
    <?php echo link_tag('tablesorter/themes/blue/style.css');?>
    <script type="text/javascript" src="<?php echo base_url(); ?>tablesorter/js/jquery.tablesorter.js"></script>
    <script type="text/javascript" src="<?php echo base_url(); ?>tablesorter/js/jquery.tablesorter.pager.js"></script>
    <script type="text/javascript">
    $(function() {
        $("table")
            .tablesorter({widthFixed: true, widgets: ['zebra']})
            .tablesorterPager({container: $("#pager")});
    });
    </script>
    <!--// Tablesorter -->

and the view where I use tablesorter is

views/countries/index.php

index.php

<table cellspacing="1" class="tablesorter">
            <thead>
                <tr>
                    <th>Country Name</th>
                    <th>Action</th>
                </tr>
            </thead>
            <tfoot>
                <tr>
                    <th>Country Name</th>
                    <th>Action</th>
                </tr>
            </tfoot>
            <tbody>
                <?php foreach ($countries as $key): ?>
                <tr>
                    <td><?php echo $key['countryName'];?></td>
                    <td><?php echo anchor("countries/edit/".$key['countryId'],"Edit")?></td>
                </tr>
                <?php endforeach; ?>
            </tbody>
        </table>
        <div id="pager" class="pager">
            <form>
                <img src="<?php echo base_url(); ?>tablesorter/icons/first.png" class="first"/> <img src="<?php echo base_url(); ?>tablesorter/icons/prev.png" class="prev"/>
                <input type="text" class="pagedisplay"/>
                <img src="<?php echo base_url(); ?>tablesorter/icons/next.png" class="next"/> <img src="<?php echo base_url(); ?>tablesorter/icons/last.png" class="last"/>
                <select class="pagesize">
                    <option selected="selected"  value="10">10</option>
                    <option value="20">20</option>
                    <option value="30">30</option>
                    <option  value="40">40</option>
                </select>
            </form>
        </div>

now after integrate with CodeIgniter it just work for ascending/descending but pagination does not work and firebug says c is undefined