I managed to break something in YUI and had that message. Clearing the cache did not fix it even after I had commented the offending section. I had to remove the fuction, allow the page to load without it, then put it back in.
Not sure if an update to YUI will help, but 0.12.2 is quite old now.
MDL-8595
General developer forum
YUI issue when rendering YAHOO.widget.Module
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