用optistruct进行topography优化分析,出现如下ERROR#79错误,寻求帮助

 错误信息如下：

*** ERROR #  79 ***

  DTPG data does not create any DVGRID data.

  There are no free referenced GRIDs.

  There may be no elements associated with the PSHELL data.

  LOAD or BOTH may be specified and all grids may be loaded.

  BC, SPC, or BOTH may be specified and all grids may be SPCed.

各参数应该都正确设置了，但还是报错，感谢好心人帮助！