求大神帮忙，hypermesh过程中发生错误，能解释下吗？

*** ERROR # 153 ***

 Exactly zero pivoting encountered during Numerical Factorization;

 the model may have rigid body mode.

  Solver error no. =   -503 

        spc set id = 6 

             index =      1 

 Possible reasons are:

 1) insufficiently constrained model,

 2) having rigid body mechanisms within the model,

 3) extremely ill-conditioned rigid element sets,

 4) extremely thin shells (as used for skinning) that have MID2/MID3,

 5) gap elements with extremely high stiffness (KA, especially KT or MU).

 Check the model and rerun the problem.

 (MECHCHECK may be used to find the rigid body modes.  To do so,

  change the input to be an eigenvalue analysis and add MECHCHECK.)

 (WARNING: results obtained with MECHCHECK cannot be used because

          the model is changed internally.)

 This error was detected in subroutine bcsmtxfct.

 This error occurs in module "lstatdrv".