If a directory is passed with -i, the -o option will overwrite the output file again and again. Therefore, all results except for the last one will be lost. To avoid it, I changed the mode "w" to "a" when opening the output file given with -o option.

Exception occurred processing file qmgr.db: Traceback (most recent call last):
  File "C:\tools\BitsParser\BitsParser.py", line 369, in process_file
    jobs = self.load_qmgr10_jobs(file_data)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\tools\BitsParser\BitsParser.py", line 319, in load_qmgr10_jobs
    jobs = self.load_qmgr10_db(file_data)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\tools\BitsParser\BitsParser.py", line 245, in load_qmgr10_db
    files_table = ese.openTable("Files")
                  ^^^^^^^^^^^^^^^^^^^^^^
  File "C:\tools\BitsParser\ese\ese.py", line 644, in openTable
    cursor['LongValues'] = self.__getLongValues(cursor['TableData']['LongValues']['FatherDataPageNumber'])
                                                ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^
KeyError: 'FatherDataPageNumber'