Matt, that is a pretty generic JS error - it could come from a number of places. When does it emerge? Is it on page load, or on a particular interaction?
If it happens on page load - you might want to start stripping out pieces of your page to see where it breaks down. I typically use the XML editor to do this hacking, by commenting out nodes of the xml . First all the javascript and action sequences, then the components, then some of the models etc. When the page loads successfully you know you’ve copied out the problem space - and you can hone your comments further.
Once you figure out where the problem happens let me know.
