anchor.diff:       ! read ndata
        call parse_next_line(unt, line, parsed_line, nfields, err)
        if (err < 0) then
  -        write(0,*) "input file can be converted to a valid checkpoint file"
  +        write(0,*) "ERROR: invalid input file"
           stop
        end if
        read(parsed_line, *, iostat=err) ndata
  
positive.code:      ! read nclasses
       call parse_next_line(unt, line, parsed_line, nfields, err)
       if (err < 0) then
          write(0,*) "input file can be converted to a valid checkpoint file"
          stop
       end if
       read(parsed_line, *, iostat=err) nclasses
  
negative.code:      ! read nvars
       call parse_next_line(unt, line, parsed_line, nfields, err)
       if (err < 0) then
          write(0,*) "ERROR: invalid input file"
          stop
       end if
       read(parsed_line, *, iostat=err) nvars
  