Second time js function not working

I have js file it have some functions
In my master page using .js file function
It working first time but if i click again that function not call in my master page
Note: “$.colorbox” function not call second time ,its undefiend

function loginpopupopen(ctrl) {
   var baseurltoaccess = '<%=GetPageFullURL("~/CartService.asmx/IsUserLoggedIn",false) %>';
            $.ajax({
                type: "POST",
                url: baseurltoaccess,
                data: "{}",
                contentType: "application/json; charset=utf-8",
                success: function(response) {
                    var result = eval(response.d);
                    if (result.retmsg == "failure") {
                        var navigationurl;
                        if ($(ctrl).attr('navigationurl').indexOf('?') == -1)
                            navigationurl = $(ctrl).attr('navigationurl') + "?";
                        else
                            navigationurl = $(ctrl).attr('navigationurl') + "&"; 
//second time not call the  "$.colorbox" its undefined
$.colorbox({ href: $('input[type=hidden][id$=hfhostname]').val() + "/" + navigationurl + "signin=1", opacity: 0.4, initialWidth: "250", initialHeight: "180", scrolling: false });
                    }
                    else
                        location.href = location.href;
                },
                dataType: "json"
            });
            
        }

Regards
Sekar.c