用Radioss算驾驶室结构自由模态出现ERROR # 160错误，怎么解决

具体出错信息如下：
*** ERROR # 160 ***
Gram-Schmidt reorthogonalization did not converge. This is caused by
ill-conditioning of the shifted matrix in Lanczos run.
(e.g. zero lower bound specified for a model with rigid body modes.)
Solver error no. = 728
subcase id = 1
This error was detected in subroutine splncz.
RAM: 309 MB total, 309 MB used.
Data arrays: 190 total, 136 allocated.
求大家帮忙。