Getting JavaScript "is not a function" error

I'm not sure of the exact cause but here is the Console error detail, hopefully that will help:

$("fieldset#edit-theme-settings", context).setSummary is not a function
attach(context=Document wfad?render=overlay)themes...?luwcz3 (line 13)
(?)()drupal.js?luwcz3 (line 55)
each(object=Object { overlayChild={...}, verticalTabs={...}, formUpdated={...}, more...}, callback=function(), args=undefined)jquery.js?v=1.5.2 (line 627)
attachBehaviors(context=Document wfad?render=overlay, settings=Object { basePath="/", ajaxPageState={...}, dev_banner={...}, more...})drupal.js?luwcz3 (line 53)
(?)()drupal.js?luwcz3 (line 365)
resolveWith(context=Document wfad?render=overlay, args=[function()])jquery.js?v=1.5.2 (line 975)
ready(wait=undefined)jquery.js?v=1.5.2 (line 414)
DOMContentLoaded()jquery.js?v=1.5.2 (line 881)
[Break On This Error] $('fieldset#edit-theme-settings', context).setSummary(function (context) {