Hi, I`m having the following error . Why am I having this error and how can I solve it?

$("SelectProject").dialog is not a function http://localhost:1419/Customer Line 57

$("#SelectProject").dialog is not a function http://localhost:1419/Customer Line 69

My codes are as follows:

$(document).ready(function() {

    $("#project_link").click(function() {
        $('SelectProject').dialog('open');
        return false;
    });

    $('#SelectProject').dialog({
        autoOpen: false,
        width: 800,
        position: [130, 200],
        buttons: {
            "Cancel": function() {
                $(this).dialog("close");
            },
            "Accept": function() {

                $(this).dialog("close");
            }
        }
    });