坛子里的高手看看这是什么错误（错误号155）

jifeilong

这是out文件的错误描述：  *** ERROR #  155 ***
Three numerical factorization in a row failed.  Probable cause
is that there is a massless mechanism in the model.
  Solver error no. =       -729
        subcase id =          3
Check the model and rerun the problem.
(osdiag,46,1 may be used to check for massless rigid body modes.)
(WARNING: results obtained with osdiag,46,1 cannot be used because
           the model is changed internally.)
This error was detected in subroutine splncz.

This error occurs in module "slvdrv".
说的不是很清楚，不知道怎样解决，请教高人赐教！