Which are the non solved problems in economic theory?

Answer 1

There is still no commonly accepted theory of business cycles. Even the role of monetary policy is disputed. There is also no good theory about economic growth that explains the differential growth rate between countries. More of less Macro Economics is composed of rules of thumb from empirical observations with no solid theoretical basis

Answer 2

Those which still could not solve Alan Greespan exposed on his new book: savage free competence with social assistence of loosers.