I have download your "FEM 679613V(iso2mesh-2021)"
I strongly advise you compute this file yourself instead of using the one I posted, in order to debug all the processing chain upstream and validate the contents of your database. If you have errors in other files, it is pointless for us to try and debug the problems you report.
when I used it to compute ISO MEG head model, it worked. But when I used it to compute DTI MEG head model, error occur
It seems unlikely that DUNEuro would check for the grid in the anisotropic case, but not in the isotropic case. Please check again what you are doing.