Have a problem with Sortable in IE

I try to create multilevel tree and sort it with ui.sortable. The
objective is to move all sublevels together with parent level. It`s ok
in Safari and FF, but not working in IE (7-8). Can someone give me an
advise?
Here is the code:
<script language="JavaScript">
$(document).ready(
function()
{
        $(".srt").sortable({
            placeholder: 'ui-state-highlight',
            revert: true
        });
}
);
</script>
<ul class="srt">
    <li>Test level 1
        <ul class="srt">
            <li>Test level 2
                <ul class="srt">
                    <li>Test level 3</li>
                    <li>Test level 3</li>
                </ul>
            </li>
            <li>Test level 2</li>
        </ul>
    </li>
    <li>Test level 1</li>
</ul>