Thank you for your quick reply 
I found that at the end of the segmentation by CAT12, the temporary folder is deleted. And after I recovered the file from the recycle bin and tried to import it, the following error occurred. It seems that something is missing.
So I have also tried the second way, which seems convenient. After the duplication, I proceeded with BEM surfaces generation and source computation. The procedures went without error. But I was confused. Is it normal to have two BEM head, outerskull, and inner skull files in one subject?
