To resolve this issue immediately, your first step should be to verify that you have the latest AutoCAD updates installed, as Autodesk frequently patches compatibility and file-reading bugs. However, depending on your system configuration, several distinct factors may be triggering this error.
C:\Program Files\Autodesk\AutoCAD 2021\
Did this error start happening or an AutoCAD update ? problem loading acadres.dll resource file autocad 2021