[jQuery] Using back button causes C.easing[e.easing || (C.easing.swing ? "swing" : "linear")] is not a function

[jQuery] Using back button causes C.easing[e.easing || (C.easing.swing ? "swing" : "linear")] is not a function


I am doing some ajax and calling a function every 5 seconds and it
works perfect except when I press the back button and then gives this
error on the next ajax load
C.easing[e.easing || (C.easing.swing ? "swing" : "linear")] is not a
function
HERE IS MY CODE
$(document).ready(function()
{
    timer_set = 0;
    prevnext();
});
function prevnext()
{
    //optional arguments, create the extra query string
    var next_param = (arguments[0]) ? '&next=' + arguments[0] :
'&next=1';
    var numsent_param = (arguments[1]) ? '&numsent=' + arguments[1] : '';
    var extraparameters = next_param + numsent_param;
    $.ajaxSetup({timeout: 5000});
    $.ajax({
        type: 'POST',
        url: 'http://example.com/request.php',
        data: 'url=' + encodeURI('http://example.com/data.xml') +
'&maxlength=' + encodeURI('3') + extraparameters,
        beforeSend: function() {
            if (timer_set)
                clearTimeout(video_ajax_timer_id);
            $('#video_ajax_gallery').empty();
            $('#video_ajax_gallery').append('<div id="ajax_loading">loading</
div>');
        },
        error: function(){
            $('#video_ajax_gallery').append('Error loading data.');
        },
        success: function(msg){
            $('#video_ajax_gallery').append('<div
id="video_gallery_container"></div>');
            $('#video_gallery_container').append(msg);
            $('#video_gallery_container').fadeOut(1,function(){
                $('#ajax_loading').hide();
            });
            $('#video_gallery_container').fadeIn('slow', function(){
                video_ajax_timer_id = setTimeout("prevnext(1, next_video_num)",
5000);//next_video_num is set in response
                timer_set = 1;
            });
        }
    });
}