You could try importing them into calibre with the stable 10.0.3 version of the
DeDRM plugin installed or you could install the latest version which seems to be stable from all reports I've seen from
10.0.9 (beta for 10.1.0)
Please note that DeDRM only works on import so if you already have the DRMmed files in calibre, you may want to drag/drop the file onto the Details pane to re-import them.