Commented Unassigned: Error: Unable to get property 'UI' of undefined or null reference [27493]

Downloaded latest version 4.5.7.725 build on 7/25/2013 and this is the error I get. It used to work on the older version.

What is the work around or fix?
Comments: Here is the javascript that is having issues: $create(Sys.Extended.UI.AccordionBehavior, {"ClientStateFieldID":"MainContent_Accordion1_AccordionExtender_ClientState","FadeTransitions":true,"FramesPerSecond":40,"HeaderCssClass":"accordionHeader","HeaderSelectedCssClass":"accordionHeaderSelected","SelectedIndex":5,"id":"MainContent_Accordion1_AccordionExtender","requireOpenedPane":false,"suppressHeaderPostbacks":true}, null, null, $get("MainContent_Accordion1"));