mesh problem

[X X]

I created my mesh with two pairs of periodic boundary conditions in ICEM and exo2nek in Nek, and it compiled correctly. But when I run, throw me the following error

 Mixed B.C. on a side nonaligned with either the X,Y, or Z axis detected for
  Element          53    side           4
  Requires STRESS FORMULATION
  Mixed B.C. on a side nonaligned with either the X,Y, or Z axis detected for
  Element          55    side           3
  Requires STRESS FORMULATION
  Mixed B.C. on a side nonaligned with either the X,Y, or Z axis detected for
  Element          56    side           3
  Requires STRESS FORMULATION

Please help me.