RoC's PC has a lot of folders and some of them have pretty long names. Windows can't really handle this very well, admittedly. Move the path of where you extracted RoC's PC (or even the PKHeX installation where the database is) up closer to root, or be more selective with the folders you add into the database (don't add it wholesale).
RoC's PC wasn't really made to be added to the PKHeX database.