"Classes must not be nested" error

If you ever come across the "classes must not be nested" error (and/or the "internal build" error) then you're in trouble :) There are different possible causes for these errors. In my case it was because I was referring to a none existing component from within an itemRenderer. A good list with a number of potential causes can be found on http://rjowen.wordpress.com/2007/06/21/internal-build-error-or-classes-must-not-be-nested-error/.