jQuery AutoComplete does not show up

Question

Inside a jquery dialog I would like to use the jquery autocomplete feature of jqueryUI.

I have then prepared an action in my Controller (I am using ASP.NET MVC2) that is as follow

public ActionResult GetForos(string startsWith, int pageSize)
{
    // get records from underlying store
    int totalCount = 0;
    string whereClause = "Foro Like '" + startsWith + "%'";
    List<Foro> allForos = _svc.GetPaged(whereClause, "Foro", 0, pageSize, out totalCount);

    //transform records in form of Json data
    List<ForoModelWS> foros = new List<ForoModelWS>();
    foreach ( Foro f in allForos)
        foros.Add( new ForoModelWS() { id= Convert.ToString(f.ForoId), 
            text= f.Foro + ", Sezione: " + f.Sezione + ", " + f.AuthorityIdSource.Name });

    return Json(foros);
}

The class ForoModelWS is a simple class used only to hold the data that shall be transferred in json. Here it is

public class ForoModelWS
{
    public string id;
    public string text;
}

On the client side I have the following jquery code:

<input id="theForo" />

<script type="text/javascript">
    $(document).ready(function() {

        $("#theForo").autocomplete({
            source: function(request, response) {
                $.ajax({
                    type: "post",
                    url: "/Foro/GetForos",
                    dataType: "json",
                    data: {
                        startsWith: request.term,
                        pageSize: 15
                    },
                    success: function(data) {
                        response($.map(data, function(item) {
                            return {
                                label: item.text,
                                value: item.text
                            }
                        }))
                    }
                })
            },
            minLength: 2,
            select: function(event, ui) {
            },
            open: function() {
                $(this).removeClass("ui-corner-all").addClass("ui-corner-top");
            },
            close: function() {
                $(this).removeClass("ui-corner-top").addClass("ui-corner-all");
            }
        });

    });
</script>

But the sliding window with the suggeestions does not appear. If I put an alert inside the response function I can see the correct data.

Do I miss something?

Thanks for helping

1st EDIT: Moreover, How to change the code to use the "id" property of the selected element in the returned list?

2nd EDIT: I have checked more with Chrome developer tool and I have seen that when autocomplete starts some error appear. the following:

Uncaught TypeError: Cannot call method 'zIndex' of undefined  @ _assets/js/jquery-ui-1.8.4.custom.min.js:317
Uncaught TypeError: Cannot read property 'element' of undefined @ _assets/js/jquery-ui-1.8.4.custom.min.js:321
Uncaught TypeError: Cannot read property 'element' of undefined @ _assets/js/jquery-ui-1.8.4.custom.min.js:320

It seems that the autocomplete plugin does not find an element when it tries to set the z-Index of the sliding suggestion 1 level up its container. The first error appear when the jquery UI Dialog opens. The input for the autocomplete is inside a jquery tab that is inside a jquery Dialog

3rd EDIT: I am adding the HTML markup to be complete

<td width="40%">
   <%= Html.LabelFor(model => model.ForoID)%>
   <br />
   <%= Html.HiddenFor(model => model.ForoID) %>
   <input id="theForo" />
   <%= Html.ValidationMessageFor(model => model.ForoID, "*")%>
</td>

Answer 1

I have found the problem.

In my case I was using also another plugin, this one.

That plugin was included at the end of my scripts and caused the error described in the question. I have removed the plugin and everything work very fine.

Before removing it I have tried also to isolate the problem putting in a static html both the scripts. I experienced that even the simplest usage of the autocomplete features, like this

<script type="text/javascript">
$(document).ready(function() {

    var availableTags = ["ActionScript", "AppleScript", "Asp", "BASIC", "C", "C++", "Clojure",
    "COBOL", "ColdFusion", "Erlang", "Fortran", "Groovy", "Haskell", "Java", "JavaScript",
    "Lisp", "Perl", "PHP", "Python", "Ruby", "Scala", "Scheme"];

    $("#theForo").autocomplete({
        source: availableTags
    });
});
</script>

would cause the error I got.

My choice has been to remove the menu plugin even because that code is'nt supported anymore.

Thanks!