Discontent is a learning barrier, so I think their criticism has to be taken seriously. TBL is a great technique, but maybe you can incorporate some changes that may make them appreciate the learning experience a little more. They are complaining about a lack of lecture, so maybe they need a little more explaining. Economics is a tough subject; maybe the students feel that the blind are leading the blind.
I think an outside observer who understands TBL could be useful. I would ask him or her to join one of the groups and participate as a student.
What you don't want is for your class to develop a negative reputation, as that could dissuade others from trying the technique.
John
