  The mistakes of the classical solution of screw dislocations in smectic-A
liquid crystals are pointed out. This reveals a serious problem of the
well-known theory, which may be named de Gennes-Kleman-Pershan paradox, for
many decades in the scientific community of liquid crystal study. The correct
solution is given in this letter in terms of simplest, elementary and
straightforward solution method. Furthermore, the stress filed and energy of
dislocation are discussed in detail. The present article gives a corrected
stress field and dislocation energy as well.
