optistruct计算 Error312 怎么解决？

optistruct计算报错如下：
************************************************************************
 A fatal error has occurred during computations:
  *** ERROR # 312 ***
  In static load case 1
  the compliance is negative or large -5.62632e+013.
  Optimization/buckling analysis cannot be performed.
  due to possible rigid body mode.
  INFEASIBLE DESIGN (AT LEAST ONE CONSTRAINT VIOLATED).
  *** SOME ERRORS WERE REPORTED DURING THE RUN,
  *** PLEASE VERIFY RESULTS AS THEY MAY BE INVALID.
  ...************************************************************************
是什么问题呢，请大神指点。