Unable to Access UpdateProgress Control via JavaScript

I am trying to display an UpdateProgress via JavaScript, however the JavaScript keeps erroring out with "Object Expected". I know that the client ID of the UpdateProgress is correct. What am I missing? I've tried both get$() and document.getElementById and single/double quotes. Per the link below, it should work. The UpdateProgress controls exist on user controls.

http://msdn.microsoft.com/en-us/library/bb398821(v=vs.100).aspx

                            function ChangeMainPanel() {
                                var qspProjectNumber = getQueryStringParameter("ProjectNumber");
                                if (qspProjectNumber.length == 0) {
                                    var URL = "Setup_Detail.aspx?savequerystring=yes&view=" + document.getElementById("DropDownListSelectMainPanel").value;                                
                                } else {
                                    var URL = "Setup_Detail.aspx?savequerystring=yes&view=" + document.getElementById("DropDownListSelectMainPanel").value + "&ProjectNumber=" + getQueryStringParameter("ProjectNumber");
                                }
                                var panel = $get("DropDownListSelectMainPanel").value;
                                window.alert(panel);
                                switch (panel) {
                                    case "PanelGeneralInformation":
                                        window.alert("PanelGeneralInformation");
                                        get$('Setup_GeneralInformation_UpdateProgressShowSetup').style.display = "block";
                                        break;
                                    case "PanelShowContacts":
                                        window.alert("PanelContacts");
                                        get$('Setup_Contacts_UpdateProgressShowSetup').style.display = "block";
                                        break;
                                    default:
                                }
                                window.location.href=URL;
                            }