[SOLVED] TypeError: ui.helper.attr(...) is undefined

[SOLVED] TypeError: ui.helper.attr(...) is undefined

I am trying to replicate the functionality mentioned in http://www.placona.co.uk/166/javascript/a-more-elaborated-jquery-drag-drop-cloning/
But, I am getting the error "TypeError: ui.helper.attr(...) is undefined" in console.
I couldn't find the answer from googling. Anyone have any idea about what might be causing this error?