We investigate numerical solutions of high order curl problems with various formulations and finite elements. We show that several classical conforming finite elements lead to spurious solutions, while mixed formulations with finite elements in complexes solve the problems correctly. To explain the numerical results, we clarify the cohomological structures in high order curl problems by relating the partial differential equations to the Hodge-Laplacian boundary problems of the grad curl-complexes.2000 Mathematics Subject Classification. 65N30 and 35Q60 and 65N15 and 35B45. Key words and phrases. H(curl 2 )-conforming, finite elements, spurious solution, de Rham complexes, exterior calculus, high order curl problems.