将igs文件导入LT出现以下问题: =U4f}W;  
 t_jyyHxoZ:  
*** Error (AITX_BLANKED_ENTS) *** *.,"N}  
  x37/cu  
The input file did not contain any supported non blanked independant entities. N;-/w ip  
  #V.ZdLo(  
Please check the documentation for a list of supported entities. |7	&|>  
 `"a? a5]k  
请教各位是什么原因,如何解决?