rdiff-backup and "Found too many current_mirror incs!"

If you use rdiff-backup or some program, which sits on top of it (e.g. backupninja) and you get errors similar to this:

Traceback (most recent call last):
File „/usr/bin/rdiff-backup“, line 23, in ?
rdiff_backup.Main.error_check_Main(sys.argv[1:])
File „/var/lib/python-support/python2.4/rdiff_backup/Main.py“, line 298, in error_check_Main
try: Main(arglist)
File „/var/lib/python-support/python2.4/rdiff_backup/Main.py“, line 318, in Main
take_action(rps)
File „/var/lib/python-support/python2.4/rdiff_backup/Main.py“, line 276, in take_action
elif action == „check-destination-dir“: CheckDest(rps[0])
File „/var/lib/python-support/python2.4/rdiff_backup/Main.py“, line 780, in CheckDest
need_check = checkdest_need_check(dest_rp)
File „/var/lib/python-support/python2.4/rdiff_backup/Main.py“, line 817, in checkdest_need_check
assert len(curmir_incs) == 2, „Found too many current_mirror incs!“
AssertionError: Found too many current_mirror incs

Then you might try to go to your rdiff-backup-data directory of your backup and delete all but the latest current-mirror-*.data files. At least my backups (simple rdiff-backup) are working again.