tablesorter in ui tab not working on IE (6 or 7)

tablesorter in ui tab not working on IE (6 or 7)


I have a ui tab layout. One of the tabs has a table which is sorted
using the tablesorter plugin. This all works perfectly on Firefox but
an error is shown on both ie6 and ie7 running on xp. The error is:
Object has no properties. If I take the tablesorter out of the tabbed
layout it works fine. Is this a bug in the ui tabs code or the
tablesorter code and if so how can I get a sorted table working in a
tabbed layout?
This is my tab calling code:
$(document).ready(function() {
    $('#mainTab > ul').tabs({ cache: true, ajaxOptions: {cache: false}});
});
and then my tab html:
<div id="mainTab">
    <ul>
        <li><a href="listUsers.cfm" title="tab1"><span>User List</span></a></
li>
    </ul>
</div>
Then in my listUsers.cfm I have the following tablesorter stuff:
<script type="text/javascript" src="assets/js/jquery/
jquery.tablesorter.pack.js"></script>
    <script type="text/javascript">
        $(document).ready(function() {
         $.tablesorter.defaults.widgets = ['zebra'];
         $("#userlist").tablesorter();
         $("#userlist > tbody > tr").click(function() {
                 var contactid = $(this).attr('id');
                 var newName = 'User Details';
                    var thePage = "editUser.cfm&contactid=" + contactid;
                    $('#mainTab > ul').tabsAdd(thePage,newName,2);
                    $('#mainTab > ul').tabsClick(2);
             }).hover(function() {
                    $(this).addClass('hover_tablerow');
                }, function() {
                     $(this).removeClass('hover_tablerow');
                });
        });
    </script>
Then my html:
<table id="userlist" class="tablesorter" width="700" cellspacing="0"
cellpadding="3" border="0">
    <thead>
        <tr>
            <th style="width: 80px;">Contact ID</th>
            <th style="width: 200px;">Username</th>
            <th style="width: 200px;">Called Name</th>
            <th style="width: 150px;">Surname</th>
            <th style="width: 150px;">Town</th>
        </tr>
    </thead>
    <tbody>
        <tr id="13">
            <td>13</td>
            <td>joe.bloggs</td>
            <td>Joe</td>
            <td>Bloggs</td>
            <td>Oxford</td>
        </tr>
    </tbody>
</table>
I can probably post a demo url if needed but has anyone seen this
problem before and have managed to fix it?
Cheers,
Dave