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Seems like there is a problem with your extensions. But since extensions are not loaded until you include a visualization based on it you should be able to localize the problem by starting with a visualization using a built-in chart or an extension you use in another mashup and if that works try with extension objects. Once you have localized the problematic extension you need to contact the extension developer.
If you cannot use any object from the app the problem is probably not the extension.
Another way forward is to open the browser console and look for errors.
Hope this helps