Autocomplete can't select on IE

Autocomplete can't select on IE

I recently installed Autocomplete and I love it. I have a "citystate" field that collects data from geonames.org via JSON. It works great on FF and Chrome, but on IE (7 and 8) I'm experiencing a frustrating problem. When I select the city/state from the list that pops up, I cannot select it. Instead, I get an Javascript error:

Message: Unexpected call to method or property access.
Line: 104
Char: 68
Code: 0

The Developer Tool says "Unexpected call to method or property access". jquery-1.4.2.min.js, line 104 character 68.

That appears to be this: {this.nodeType===1&&this.insertBefore(a,this.firstChild)})

Here's my input:
<input id="citystate" tabindex="3" class="ui-widget input required pageRequired" maxlength="150" size="30" />

And here's the function (practically taken out of the demo):

        $("#citystate").autocomplete({
                source: function(request, response) {
                        $.ajax({
                                url: "http://ws.geonames.org/searchJSON",
                                dataType: "jsonp",
                                data: {
                                        featureClass: "P",
                                        style: "full",
                                        maxRows: 12,
                                        country: "US",
                                        name_startsWith: request.term
                                },
                                success: function(data) {
                                        response($.map(data.geonames, function(item) {
                                                return {
                                                        label: item.name + (item.adminName1 ? ", " + item.adminName1 : ""),
                                                        value: item.name + ", " + item.adminName1
                                                }
                                        }))
                                }
                        })
                },
                minLength: 2,
                select: function(event, ui) {
                        log(ui.item ? (ui.item.label) : "Nothing selected, input was " + this.value);
                },
                open: function() {
                        $(this).removeClass("ui-corner-all").addClass("ui-corner-top");
                },
                close: function() {
                        $(this).removeClass("ui-corner-top").addClass("ui-corner-all");
                }
        });


I've tried different versions of jQuery and different DOCTYPEs. Nothing seems to help. Does anyone have any ideas?

Thanks!